403 Forbidden vs 401 Unauthorized HTTP responses

Question

For a web page that exists  but for which a user does not have sufficient privileges  they are not logged in or do not belong to the proper user group   what is the proper HTTP response to serve   401 Unauthorized  403 Forbidden  Something else   What I ve read on each so far isn t very clear on the difference between the two  What use cases are appropriate for each response

User · Answer

I think it is important to consider that, to a browser, 401 initiates an authentication dialog for the user to enter new credentials, while 403 does not. Browsers think that, if a 401 is returned, then the user should re-authenticate. So 401 stands for invalid authentication while 403 stands for a lack of permission.

Here are some cases under that logic where an error would be returned from authentication or authorization, with important phrases bolded.

A resource requires authentication but no credentials were specified.

401: The client should specify credentials.

The specified credentials are in an invalid format.

400: That's neither 401 nor 403, as syntax errors should always return 400.

The specified credentials reference a user which does not exist.

401: The client should specify valid credentials.

The specified credentials are invalid but specify a valid user (or don't specify a user if a specified user is not required).

401: Again, the client should specify valid credentials.

The specified credentials have expired.

401: This is practically the same as having invalid credentials in general, so the client should specify valid credentials.

The specified credentials are completely valid but do not suffice the particular resource, though it is possible that credentials with more permission could.

403: Specifying valid credentials would not grant access to the resource, as the current credentials are already valid but only do not have permission.

The particular resource is inaccessible regardless of credentials.

403: This is regardless of credentials, so specifying valid credentials cannot help.

The specified credentials are completely valid but the particular client is blocked from using them.

403: If the client is blocked, specifying new credentials will not do anything.

User · Answer

-----------------------     RESOURCE EXISTS    if private it is often checked AFTER auth check     -----------------------                NO         v YES     v       -----------------------    404       IS LOGGED-IN    authenticated  aka has session or JWT cookie     or       -----------------------    401                            403     NO                  YES    3xx        v              v               401             -----------------------         404 no reveal          CAN ACCESS RESOURCE    permission  authorized                     or              -----------------------              redirect                                      to login       NO                YES                                                                              v            v                                403          OK 200  redirect                             or 404  no reveal                         or 404  resource does not exist if private                         or 3xx  redirection    Checks are usually done in this order    404 if resource is public and does not exist or 3xx redirection OTHERWISE  401 if not logged-in or session expired 403 if user does not have permission to access resource  file  json       404 if resource does not exist or not willing to reveal anything  or 3xx redirection   UNAUTHORIZED  Status code  401  indicating that the request requires authentication  usually this means user needs to be logged-in  session   User agent unknown by the server  Can repeat with other credentials  NOTE  This is confusing as this should have been named  unauthenticated  instead of  unauthorized   This can also happen after login if session expired  Special case  Can be used instead of 404 to avoid revealing presence or non-presence of resource  credits  gingerCodeNinja   FORBIDDEN  Status code  403  indicating the server understood the request but refused to fulfill it  User agent known by the server but has insufficient credentials  Repeating request will not work  unless credentials changed  which is very unlikely in a short time span  Special case  Can be used instead of 404 to avoid revealing presence or non-presence of resource  credits  gingerCodeNinja   NOT FOUND  Status code  404  indicating that the requested resource is not available  User agent known but server will not reveal anything about the resource  does as if it does not exist  Repeating will not work  This is a special use of 404  github does it for example    As mentioned by  ChrisH there are a few options for redirection 3xx  301  302  303  307 or not redirecting at all and using a 401     Difference between HTTP redirect codes How long do browsers cache HTTP 301s  What is correct HTTP status code when redirecting to a login page  What  39 s the difference between a 302 and a 307 redirect

User · Answer

A clear explanation from Daniel Irvine      There s a problem with 401 Unauthorized  the HTTP status code for authentication errors  And that   s just it  it   s for authentication  not authorization    Receiving a 401 response is the server telling you     you aren   t   authenticated   either not authenticated at all or authenticated   incorrectly   but please reauthenticate and try again     To help you out    it will always include a WWW-Authenticate header that describes how   to authenticate       This is a response generally returned by your web server  not your web   application       It   s also something very temporary  the server is asking you to try   again       So  for authorization I use the 403 Forbidden response  It   s   permanent  it   s tied to my application logic  and it   s a more concrete   response than a 401       Receiving a 403 response is the server telling you     I   m sorry  I know   who you are   I believe who you say you are   but you just don   t have   permission to access this resource  Maybe if you ask the system   administrator nicely  you   ll get permission  But please don   t bother   me again until your predicament changes          In summary  a 401 Unauthorized response should be used for missing   or bad authentication  and a 403 Forbidden response should be used   afterwards  when the user is authenticated but isn   t authorized to   perform the requested operation on the given resource    Another nice pictorial format of how http status codes should be used

User · Answer

These are the meanings   401  User not  correctly  authenticated  the resource page require authentication  403  User authenticated  but his role or permissions does not allow to access requested resource  for instance user is not an administrator and requested page is for administrators

User · Answer

This is an older question  but one option that was never really brought up was to return a 404  From a security perspective  the highest voted answer suffers from a potential information leakage vulnerability  Say  for instance  that the secure web page in question is a system admin page  or perhaps more commonly  is a record in a system that the user doesn t have access to  Ideally you wouldn t want a malicious user to even know that there s a page   record there  let alone that they don t have access  When I m building something like this  I ll try to record unauthenticate   unauthorized requests in an internal log  but return a 404   OWASP has some more information about how an attacker could use this type of information as part of an attack

User · Answer

This question was asked some time ago  but people s thinking moves on  Section 6 5 3 in this draft  authored by Fielding and Reschke  gives status code 403 a slightly different meaning to the one documented in RFC 2616  It reflects what happens in authentication  amp  authorization schemes employed by a number of popular web-servers and frameworks  I ve emphasized the bit I think is most salient   6 5 3   403 Forbidden The 403  Forbidden  status code indicates that the server understood    the request but refuses to authorize it   A server that wishes to    make public why the request has been forbidden can describe that    reason in the response payload  if any   If authentication credentials were provided in the request  the server considers them insufficient to grant access   The client SHOULD NOT repeat the request with the same credentials   The client MAY repeat the request with new or different credentials   However  a request might be forbidden for reasons unrelated to the credentials  An origin server that wishes to  quot hide quot  the current existence of a forbidden target resource MAY instead respond with a status code of 404  Not Found    Whatever convention you use  the important thing is to provide uniformity across your site   API

User · Answer

they are not logged in or do not belong to the proper user group   You have stated two different cases  each case should have a different response    If they are not logged in at all you should return 401 Unauthorized If they are logged in but don t belong to the proper user group  you should return 403 Forbidden   Note on the RFC based on comments received to this answer   If the user is not logged in they are un-authenticated  the HTTP equivalent of which is 401 and is misleadingly called Unauthorized in the RFC  As section 10 4 2 states for 401 Unauthorized       The request requires user authentication     If you re unauthenticated  401 is the correct response  However if you re unauthorized  in the semantically correct sense  403 is the correct response

User · Answer

In English   401     You are potentially allowed access but for some reason on this request you were   denied  Such as a bad password  Try again  with the correct request   you will get a success response instead    403     You are not  ever  allowed  Your name is not on the list  you won t   ever get in  go away  don t send a re-try request  it will be refused    always  Go away

User · Answer

According to RFC 2616  HTTP 1 1  403 is sent when      The server understood the request  but is refusing to fulfill it  Authorization will not help and the request SHOULD NOT be repeated  If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled  it SHOULD describe the reason for the refusal in the entity  If the server does not wish to make this information available to the client  the status code 404  Not Found  can be used instead   In other words  if the client CAN get access to the resource by authenticating  401 should be sent

User · Answer

This is simpler in my head than anywhere here  so   401  You need HTTP basic auth to see this   403  You can t see this  and HTTP basic auth won t help   If the user just needs to log in using you site s standard HTML login form  401 would not be appropriate because it is specific to HTTP basic auth   I don t recommend using 403 to deny access to things like  includes  because as far as the web is concerned  those resources don t exist at all and should therefore 404   This leaves 403 as  you need to be logged in    In other words  403 means  this resource requires some form of auth other than HTTP basic auth    https   www w3 org Protocols rfc2616 rfc2616-sec10 html sec10 4 2

User · Answer

Given the latest RFC s on the matter  7231 and 7235  the use-case seems quite clear  italics added     401 is for unauthenticated   lacks valid authentication    i e   I don t know who you are  or I don t trust you are who you say you are        401 Unauthorized      The 401  Unauthorized  status code indicates that the request has not      been applied because it lacks valid authentication credentials for      the target resource   The server generating a 401 response MUST send      a WWW-Authenticate header field  Section 4 1  containing at least one      challenge applicable to the target resource       If the request included authentication credentials  then the 401      response indicates that authorization has been refused for those      credentials   The user agent MAY repeat the request with a new or      replaced Authorization header field  Section 4 2    If the 401      response contains the same challenge as the prior response  and the      user agent has already attempted authentication at least once  then      the user agent SHOULD present the enclosed representation to the      user  since it usually contains relevant diagnostic information     403 is for unauthorized   refuses to authorize    i e   I know who you are  but you don t have permission to access this resource        403 Forbidden      The 403  Forbidden  status code indicates that the server understood      the request but refuses to authorize it   A server that wishes to      make public why the request has been forbidden can describe that      reason in the response payload  if any        If authentication credentials were provided in the request  the      server considers them insufficient to grant access   The client      SHOULD NOT automatically repeat the request with the same      credentials   The client MAY repeat the request with new or different      credentials   However  a request might be forbidden for reasons      unrelated to the credentials       An origin server that wishes to  hide  the current existence of a      forbidden target resource MAY instead respond with a status code of      404  Not Found

User · Answer

Something the other answers are missing is that it must be understood that Authentication and Authorization in the context of RFC 2616 refers ONLY to the HTTP Authentication protocol of RFC 2617  Authentication by schemes outside of RFC2617 is not supported in HTTP status codes and are not considered when deciding whether to use 401 or 403  Brief and Terse Unauthorized indicates that the client is not RFC2617 authenticated and the server is initiating the authentication process  Forbidden indicates either that the client is RFC2617 authenticated and does not have authorization or that the server does not support RFC2617 for the requested resource  Meaning if you have your own roll-your-own login process and never use HTTP Authentication  403 is always the proper response and 401 should never be used  Detailed and In-Depth From RFC2616  10 4 2 401 Unauthorized The request requires user authentication  The response MUST include a WWW-Authenticate header field  section 14 47  containing a challenge applicable to the requested resource  The client MAY repeat the request with a suitable Authorization header field  section 14 8    and  10 4 4 403 Forbidden The server understood the request but is refusing to fulfil it  Authorization will not help and the request SHOULD NOT be repeated   The first thing to keep in mind is that  quot Authentication quot  and  quot Authorization quot  in the context of this document refer specifically to the HTTP Authentication protocols from RFC 2617  They do not refer to any roll-your-own authentication protocols you may have created using login pages  etc  I will use  quot login quot  to refer to authentication and authorization by methods other than RFC2617 So the real difference is not what the problem is or even if there is a solution  The difference is what the server expects the client to do next  401 indicates that the resource can not be provided  but the server is REQUESTING that the client log in through HTTP Authentication and has sent reply headers to initiate the process  Possibly there are authorizations that will permit access to the resource  possibly there are not  but let s give it a try and see what happens  403 indicates that the resource can not be provided and there is  for the current user  no way to solve this through RFC2617 and no point in trying  This may be because it is known that no level of authentication is sufficient  for instance because of an IP blacklist   but it may be because the user is already authenticated and does not have authority  The RFC2617 model is one-user  one-credentials so the case where the user may have a second set of credentials that could be authorized may be ignored  It neither suggests nor implies that some sort of login page or other non-RFC2617 authentication protocol may or may not help - that is outside the RFC2616 standards and definition   Edit  RFC2616 is obsolete  see RFC7231 and RFC7235

User · Answer

Assuming HTTP authentication  WWW-Authenticate and Authorization headers  is in use  if authenticating as another user would grant access to the requested resource  then 401 Unauthorized should be returned   403 Forbidden is used when access to the resource is forbidden to everyone or restricted to a given network or allowed only over SSL  whatever as long as it is no related to HTTP authentication   If HTTP authentication is not in use and the service a cookie-based authentication scheme as is the norm nowadays  then a 403 or a 404 should be returned   Regarding 401  this is from RFC 7235  Hypertext Transfer Protocol  HTTP 1 1   Authentication       3 1  401 Unauthorized      The 401  Unauthorized  status code indicates that the request has   not    been applied because it lacks valid authentication credentials   for    the target resource   The origin server MUST send a   WWW-Authenticate    header field  Section 4 4  containing at least one   challenge    applicable to the target resource   If the request   included    authentication credentials  then the 401 response   indicates that    authorization has been refused for those   credentials   The client MAY    repeat the request with a new or   replaced Authorization header field     Section 4 1    If the 401   response contains the same challenge as    the prior response  and the   user agent has already attempted    authentication at least once  then   the user agent SHOULD present the    enclosed representation to the   user  since it usually contains    relevant diagnostic information    The semantics of 403  and 404  have changed over time  This is from 1999  RFC 2616       10 4 4 403 Forbidden      The server understood the request  but is refusing to fulfill it    Authorization will not help and the request SHOULD NOT be repeated    If the request method was not HEAD and the server wishes to make   public why the request has not been fulfilled  it SHOULD describe the    reason for the refusal in the entity   If the server does not wish to    make this information available to the client  the status code 404    Not Found  can be used instead    In 2014 RFC 7231  Hypertext Transfer Protocol  HTTP 1 1   Semantics and Content  changed the meaning of 403      6 5 3  403 Forbidden      The 403  Forbidden  status code indicates that the server   understood    the request but refuses to authorize it   A server that   wishes to    make public why the request has been forbidden can   describe that    reason in the response payload  if any        If authentication credentials were provided in the request  the   server considers them insufficient to grant access   The client   SHOULD NOT automatically repeat the request with the same   credentials   The client MAY repeat the request with new or different    credentials   However  a request might be forbidden for reasons   unrelated to the credentials       An origin server that wishes to  hide  the current existence of a   forbidden target resource MAY instead respond with a status code of   404  Not Found     Thus  a 403  or a 404  might now mean about anything  Providing new credentials might help    or it might not   I believe the reason why this has changed is RFC 2616 assumed HTTP authentication would be used when in practice today s Web apps build custom authentication schemes using for example forms and cookies

User · Answer

TL DR   401  A refusal that has to do with authentication 403  A refusal that has NOTHING to do with authentication   Practical Examples  If apache requires authentication  via  htaccess   and you hit Cancel  it will respond with a 401 Authorization Required  If nginx finds a file  but has no access rights  user group  to read access it  it will respond with 403 Forbidden  RFC  2616 Section 10   401 Unauthorized  10 4 2   Meaning 1  Need to authenticate     The request requires user authentication        Meaning 2  Authentication insufficient         If the request already included Authorization credentials  then the 401 response indicates that authorization has been refused for those credentials        403 Forbidden  10 4 4   Meaning  Unrelated to authentication         Authorization will not help       More details       The server understood the request  but is refusing to fulfill it      It SHOULD describe the reason for the refusal in the entity     The status code 404  Not Found  can be used instead     If the server wants to keep this information from client

User · Answer

See RFC2616   401 Unauthorized      If the request already included Authorization credentials  then the 401 response indicates that authorization has been refused for those credentials    403 Forbidden      The server understood the request  but is refusing to fulfill it    Update  From your use case  it appears that the user is not authenticated  I would return 401     Edit  RFC2616 is obsolete  see RFC7231 and RFC7235

User · Answer

In the case of 401 vs 403  this has been answered many times  This is essentially a  HTTP request environment  debate  not an  application  debate   There seems to be a question on the roll-your-own-login issue  application    In this case  simply not being logged in is not sufficient to send a 401 or a 403  unless you use HTTP Auth vs a login page  not tied to setting HTTP Auth   It sounds like you may be looking for a  201 Created   with a roll-your-own-login screen present  instead of the requested resource  for the application-level access to a file  This says     I heard you  it s here  but try this instead  you are not allowed to see it

User · Answer

401 Unauthorized  I don t know who you are  This an authentication error    403 Forbidden  I know who you are  but you don t have permission to access this resource  This is an authorization error

[http-headers] 403 Forbidden vs 401 Unauthorized HTTP responses

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