Difference between revisions of "ModSecurity CRS RuleID-960911"

906911

Invalid HTTP Request Line

Validate request line against the format specified in the HTTP RFC

4 - Warning

SecRule REQUEST_LINE "!^(?:(?:[a-z]{3,10}\s+(?:\w{3,7}?://[\w\-\./]*(?::\d+)?)?/[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?|connect (?:\d{1,3}\.){3}\d{1,3}\.?(?::\d+)?|options \*)\s+[\w\./]+|get /[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?)$" \
   "phase:1,t:none,t:lowercase,block,msg:'Invalid HTTP Request Line',id:'960911',severity:'4',rev:'2.2.0',logdata:'%{request_line}',tag:'https://www.owasp.org/index.php/ModSecurity_CRS_RuleID-%{tx.id}',tag:'http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.2.1',tag:'RULE_ACCURACY_LEVEL/5',setvar:'tx.msg=%{rule.msg}',setvar:'tx.id=%{rule.id}',setvar:tx.anomaly_score=+%{tx.notice_anomaly_score},setvar:tx.protocol_violation_score=+%{tx.notice_anomaly_score},setvar:'tx.%{rule.id}-PROTOCOL_VIOLATION/INVALID_REQ-%{matched_var_name}=%{matched_var}'"

• Uses rule negation against the regex for positive security. The regex specifies the proper construction of URI request lines such as:

"http:" "//" host [ ":" port ] [ abs_path [ "?" query ]] 

• It also outlines proper construction for CONNECT, OPTIONS and GET requests.

///  A description of the regular expression:
///  
///  Beginning of line or string
///  Match expression but don't capture it. [(?:[a-z]{3,10}\s+(?:\w{3,7}?://[\w\-\./]*(?::\d+)?)?/[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?|connect (?:\d{1,3}\.){3}\d{1,3}\.?(?::\d+)?|options \*)\s+[\w\./]+|get /[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?]
///      Select from 2 alternatives
///          (?:[a-z]{3,10}\s+(?:\w{3,7}?://[\w\-\./]*(?::\d+)?)?/[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?|connect (?:\d{1,3}\.){3}\d{1,3}\.?(?::\d+)?|options \*)\s+[\w\./]+
///              Match expression but don't capture it. [[a-z]{3,10}\s+(?:\w{3,7}?://[\w\-\./]*(?::\d+)?)?/[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?|connect (?:\d{1,3}\.){3}\d{1,3}\.?(?::\d+)?|options \*]
///                  Select from 3 alternatives
///                      [a-z]{3,10}\s+(?:\w{3,7}?://[\w\-\./]*(?::\d+)?)?/[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?
///                          Any character in this class: [a-z], between 3 and 10 repetitions
///                          Whitespace, one or more repetitions
///                          Match expression but don't capture it. [\w{3,7}?://[\w\-\./]*(?::\d+)?], zero or one repetitions
///                              \w{3,7}?://[\w\-\./]*(?::\d+)?
///                                  Alphanumeric, between 3 and 7 repetitions, as few as possible
///                                  ://
///                                  Any character in this class: [\w\-\./], any number of repetitions
///                                  Match expression but don't capture it. [:\d+], zero or one repetitions
///                                      :\d+
///                                          :
///                                          Any digit, one or more repetitions
///                          /
///                          Any character that is NOT in this class: [?#], any number of repetitions
///                          Match expression but don't capture it. [\?[^#\s]*], zero or one repetitions
///                              \?[^#\s]*
///                                  Literal ?
///                                  Any character that is NOT in this class: [#\s], any number of repetitions
///                          Match expression but don't capture it. [#[\S]*], zero or one repetitions
///                              #[\S]*
///                                  #
///                                  Any character in this class: [\S], any number of repetitions
///                      connect (?:\d{1,3}\.){3}\d{1,3}\.?(?::\d+)?
///                          connect
///                          Space
///                          Match expression but don't capture it. [\d{1,3}\.], exactly 3 repetitions
///                              \d{1,3}\.
///                                  Any digit, between 1 and 3 repetitions
///                                  Literal .
///                          Any digit, between 1 and 3 repetitions
///                          Literal ., zero or one repetitions
///                          Match expression but don't capture it. [:\d+], zero or one repetitions
///                              :\d+
///                                  :
///                                  Any digit, one or more repetitions
///                      options \*
///                          options
///                          Space
///                          Literal *
///              Whitespace, one or more repetitions
///              Any character in this class: [\w\./], one or more repetitions
///          get /[^?#]*(?:\?[^#\s]*)?(?:#[\S]*)?
///              get
///              Space
///              /
///              Any character that is NOT in this class: [?#], any number of repetitions
///              Match expression but don't capture it. [\?[^#\s]*], zero or one repetitions
///                  \?[^#\s]*
///                      Literal ?
///                      Any character that is NOT in this class: [#\s], any number of repetitions
///              Match expression but don't capture it. [#[\S]*], zero or one repetitions
///                  #[\S]*
///                      #
///                      Any character in this class: [\S], any number of repetitions
///  End of line or string

Here is an example payloads taken from HTTPrint (http://net-square.com/httprint/) that will trigger this rule.

127.0.0.1 - - [14/Sep/2010:11:51:43 -0400] "\x16\x03" 501 214 TI@aD8CoAWYAAAOFHNMAAACA

Include an example ModSecurity Audit Log Entry for when this rule matchs.

--1167a167-A--
[14/Sep/2010:11:51:43 --0400] TI@aD8CoAWYAAAOFHNMAAACA 127.0.0.1 51285 127.0.0.1 80
--1167a167-B--
^V^C

--1167a167-F--

--1167a167-H--
Message: Match of "rx ^(?:(?:[a-z]{3,10}\\s+(?:\\w{3,7}?://[\\w\\-\\./]*(?::\\d+)?)?/[^?#]*(?:\\?[^#\\s]*)?(?:#[\\S]*)?|connect (?:\\d{1,3}\\.){3}\\d{1,3}\\.?(?::\\d+)?|options \\*)\\s+[\\w\\./]+|get /[^?#]*(?:\\?[^#\\s]*)?(?:#[\\S]*)?)$" 
against "REQUEST_LINE" required. [file "/usr/local/apache/conf/modsec_current/base_rules/modsecurity_crs_20_protocol_violations.conf"] [line "34"] [id "960911"] [rev "2.0.8"] [msg "Invalid HTTP Request Line"] [severity "WARNING"] 
[tag "http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.2.1"]
Apache-Error: [file "core.c"] [line 3773] [level 3] Invalid method in request \\x16\\x03
Stopwatch: 1284479503453580 43606 (4888 42377 -)
Producer: ModSecurity for Apache/2.5.12 (http://www.modsecurity.org/); core ruleset/2.0.8.
Server: Apache/2.2.12 (Unix) mod_ssl/2.2.12 OpenSSL/0.9.8l DAV/2

--1167a167-Z--

Some malformed URIs are created on purpose as part of HTTP fingerprinting scans -

http://projects.webappsec.org/Fingerprinting

Other times, these are caused by poorly written web clients.

Easy

Easy with either regular expressions or by monitoring Apache error logging in phase:5

None known
If there are any known false positives - specify them here Also sign-up for the Reporting False Positives mail-list here: https://lists.sourceforge.net/lists/listinfo/mod-security-report-false-positives
Send FP Report emails here:
mod-security-report-false-positiveslists.sourceforge.net

None known

5
5 point scale where:
1 = Beta/Experimental and/or high number of false positives reported
5 = Strong Rule and/or no false positives reported

Ryan Barnett - ryan.barnettowasp.org

http://www.w3.org/Protocols/rfc2616/rfc2616-sec3.html#sec3.2.1