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Squid 3.2.7 DoS (loop, 100% cpu) strHdrAcptLangGetItem() at errorpage.cc
From: tytusromekiatomek () hushmail com
Date: Tue, 05 Mar 2013 20:54:04 +0000

################################################################
# DoS (loop, 100% cpu) strHdrAcptLangGetItem() at errorpage.cc #
################################################################
#
# Authors:
#
# 22733db72ab3ed94b5f8a1ffcde850251fe6f466
# c8e74ebd8392fda4788179f9a02bb49337638e7b
# AKAT-1
#
#######################################

# Versions: 3.2.5, 3.2.7 


  This error is only triggered when squid needs to generate an error page (for example backend node is not responding 
etc...)
  POC (request):
  -- cut --
  GET http://127.0.0.1:1/foo HTTP/1.1
  Accept-Language: ,
  -- cut --

  e.g : curl -H "Accept-Language: ," http://localhost:3129/

  Code:

    strHdrAcptLangGetItem is called with pos equals 0, therefore first branch
    in if (316 line) is taken, because xisspace(hdr[pos]) is false, then pos++
    is not executed (because hdr[0] is ','). In 335 line statement in while is
    also false because hdr[0] = ',', so whole loop body is omited. dt = lang,
    thus after assignment in 353 line *lang == '\0', so expression in if
    statement in 357 line is false. So next execution of while body (314 line),
    has got same preconditions as previous, thus it's infinite loop.

   312  bool strHdrAcptLangGetItem(const String &hdr, char *lang, int langLen, size_t &pos)
   313  {
   314      while (pos < hdr.size()) {
   315          char *dt = lang;

   316          if (!pos) {
   317              /* skip any initial whitespace. */
   318              while (pos < hdr.size() && xisspace(hdr[pos]))
   319                  ++pos;
   320          } else {
   321              // IFF we terminated the tag on whitespace or ';' we need to skip to the next ',' or end of header.
   322              while (pos < hdr.size() && hdr[pos] != ',')
   323                  ++pos;
   324              if (hdr[pos] == ',')
   325                  ++pos;
   326          }

   327          /*
   328           * Header value format:
   329           *  - sequence of whitespace delimited tags
   330           *  - each tag may suffix with ';'.* which we can ignore.
   331           *  - IFF a tag contains only two characters we can wildcard ANY translations matching: <it> '-'? .*
   332           *    with preference given to an exact match.
   333           */
   334          bool invalid_byte = false;
   335          while (pos < hdr.size() && hdr[pos] != ';' && hdr[pos] != ',' && !xisspace(hdr[pos]) && dt < (lang + 
(langLen -1)) ) {
   336              if (!invalid_byte) {
   337  #if USE_HTTP_VIOLATIONS
   338                  // if accepting violations we may as well accept some broken browsers
   339                  //  which may send us the right code, wrong ISO formatting.
   340                  if (hdr[pos] == '_')
   341                      *dt = '-';
   342                  else
   343  #endif
   344                      *dt = xtolower(hdr[pos]);
   345                  // valid codes only contain A-Z, hyphen (-) and *
   346                  if (*dt != '-' && *dt != '*' && (*dt < 'a' || *dt > 'z') )
   347                      invalid_byte = true;
   348                  else
   349                      ++dt; // move to next destination byte.
   350              }
   351              ++pos;
   352          }
   353          *dt = '\0'; // nul-terminated the filename content string before system use.
   354          ++dt;

   355          debugs(4, 9, HERE << "STATE: dt='" << dt << "', lang='" << lang << "', pos=" << pos << ", buf='" << 
((pos < hdr.size()) ? hdr.substr(pos,hdr.size()) : "") << "'");

   356          /* if we found anything we might use, try it. */
   357          if (*lang != '\0' && !invalid_byte)
   358              return true;
   359      }
   360      return false;
   361  }

EOF

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