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hackeroneJalioH1:287667
HistoryNov 06, 2017 - 9:13 a.m.

Internet Bug Bounty: CVE-2017-13090 wget heap smash

2017-11-0609:13:11
jalio
hackerone.com
48

0.399 Low

EPSS

Percentile

97.3%

The retr.c:fd_read_body() function is called when processing OK responses. When the response is sent chunked in wget before 1.19.2, the chunk parser uses strtol() to read each chunk’s length, but doesn’t check that the chunk length is a non-negative number. The code then tries to read the chunk in pieces of 8192 bytes by using the MIN() macro, but ends up passing the negative chunk length to retr.c:fd_read(). As fd_read() takes an int argument, the high 32 bits of the chunk length are discarded, leaving fd_read() with a completely attacker controlled length argument. The attacker can corrupt malloc metadata after the allocated buffer.

Reproduction
To reproduce, use two terminals. In the first terminal:
$ nc -l -p 8080 <wget-heap-smash.reply
In the second terminal:
$ wget http://127.0.0.1:8080/foo

Depending on how wget is compiled, this will either simply segfault or
complain about the heap being corrupted.

External Links
https://nvd.nist.gov/vuln/detail/CVE-2017-13090
http://git.savannah.gnu.org/cgit/wget.git/commit?id=ba6b44f6745b14dce414761a8e4b35d31b176bba
http://www.debian.org/security/2017/dsa-4008
http://www.securityfocus.com/bid/101590
http://www.securitytracker.com/id/1039661
https://www.viestintavirasto.fi/en/cybersecurity/vulnerabilities/2017/haavoittuvuus-2017-037.html