The clientAbortBody function in client_side.c in Squid Web Proxy Cache before 2.6 STABLE6 allows remote attackers to cause a denial of service (segmentation fault) via unspecified vectors that trigger a null dereference.  NOTE: in a followup advisory, a researcher claimed that the issue was a buffer overflow that was not fixed in STABLE6. However, the vendor's bug report clearly shows that the researcher later retracted this claim, because the tested product was actually STABLE5.