oss-sec mailing list archives
Re: CVE Request: lighttpd/mod_auth out-of-bounds read due to signedness error
From: Kurt Seifried <kseifried () redhat com>
Date: Tue, 29 Nov 2011 14:27:33 -0700
On 11/29/2011 06:25 AM, Stefan Bühler wrote:
Hi, Xi Wang discovered the following issue in lighttpd: for http auth we need to base64-decode user input; the allowed character range includes non ASCII characters above 0x7f. The function to decode this string takes a "const char *in"; and reads each character into an "int ch", which is used as offset in the table. So characters above 0x7f lead to negative indices (as char is signed on most platforms). Here the vulnerable code (src/http_auth.c:67) --- static const short base64_reverse_table[256] = ...; static unsigned char * base64_decode(buffer *out, const char *in) { ... int ch, ...; size_t i; ... ch = in[i]; ... ch = base64_reverse_table[ch]; ... } --- It doesn't matter if "broken" data is read - it just may allow more encodings of the correct login information. The only possible impact is a segfault, leading to DoS. I had a look at some debian and openSUSE binaryies, and it looks like there is always enough data (>= 256 bytes) in the .rodata section before the base64_reverse_table table, so these binaries are not vulnerable afaict. we plan to release 1.4.30 soon, including the fix for this issue. regards, stefan bug tracked as: http://redmine.lighttpd.net/issues/2370 announcement (not complete yet): http://download.lighttpd.net/lighttpd/security/lighttpd_sa_2011_01.txt proposed patch === diff --git a/src/http_auth.c b/src/http_auth.c index f2f86dd..33adf71 100644 --- a/src/http_auth.c +++ b/src/http_auth.c @@ -99,7 +99,7 @@ static unsigned char * base64_decode(buffer *out, const char *in) { ch = in[0]; /* run through the whole string, converting as we go */ for (i = 0; i < in_len; i++) { - ch = in[i]; + ch = (unsigned char) in[i]; if (ch == '\0') break; ===
Please use CVE-2011-4362 for this issue. -- -Kurt Seifried / Red Hat Security Response Team
Current thread:
- CVE Request: lighttpd/mod_auth out-of-bounds read due to signedness error Stefan Bühler (Nov 29)
- Re: CVE Request: lighttpd/mod_auth out-of-bounds read due to signedness error Kurt Seifried (Nov 29)