SpamAssassin / spamc+BSMTP remote buffer overflow

2003-01-24T00:00:00
ID SECURITYVULNS:DOC:4023
Type securityvulns
Reporter Securityvulns
Modified 2003-01-24T00:00:00

Description

Well, I was going to wait until 2.50 release, but it seems to be taking and this likely affects only few installations. Besides, it's been in their public bugzilla for over a month. So:

Attacker may be able to execute arbitrary code by sending a specially crafted e-mail to a system using SpamAssassin's spamc program in BSMTP mode (-B option). Versions from 2.40 to 2.43 are affected.

Exim users especially should check if they're affected, the -B option is used in several Exim+SpamAssassin HOWTOs.

The problem is with escaping '.' characters at the beginning of lines. Off-by-one bounds checking error allows writing '.' character past a buffer, overwriting the stack frame address. Depending on system this may be exploitable. Pre-built Debian unstable/x86 package wasn't vulnerable, my self compiled was.

Patch:

diff -ru spamassassin-2.43-old/spamd/libspamc.c spamassassin-2.43/spamd/libspamc.c --- spamassassin-2.43-old/spamd/libspamc.c 2002-10-15 18:22:49.000000000 +0300 +++ spamassassin-2.43/spamd/libspamc.c 2002-12-27 20:19:36.000000000 +0200 @@ -309,7 +309,7 @@ case MESSAGE_BSMTP: total=full_write(fd, m->pre, m->pre_len); for(i=0; i<m->out_len; ){ - for(j=0; i<m->out_len && j<sizeof(buffer)/sizeof(buffer)-1; ){ + for(j=0; i<m->out_len && j<sizeof(buffer)/sizeof(buffer)-2; ){ if(i+1<m->out_len && m->out[i]=='\n' && m->out[i+1]=='.'){ buffer[j++]=m->out[i++]; buffer[j++]=m->out[i++];