PHP Error "canary mismatch on efree"

Question

A strange error appeared in the error log in PHP, but the script that generated this error is often used and never generated this error, and occurred only once so far. Would anyone tell me why this happened?

Error: [client {some IP}] ALERT - canary mismatch on efree() - heap overflow detected (attacker '{some IP}', file '{some script php}')

My server: Apache/2.2.13 (FreeBSD) mod_ssl/2.2.13 OpenSSL/0.9.8k DAV/2 PHP/5.2.11 with Suhosin-Patch with PHP 5.2.11

Answer 1

It means that Suhosin detected a bug in PHP:

http://web.archive.org/web/20140217234227/http://www.suspekt.org/2008/10/12/suhosin-canary-mismatch-on-efree-heap-overflow-detected

Answer 2

Seems like a log entry without the data. Probably a malformed header which was not detected correctly.

Answer 3

The problem is in Suhosin-Patch. Some code structures causes such error. Either remove suhosin patch either try to figure out which part of the code causes such error.