#VU46310 Use-after-free in GNU Bison - CVE-2020-24240

Vulnerability identifier: #VU46310

Vulnerability risk: Medium

CVSSv4.0: 4.6 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2020-24240

CWE-ID: CWE-416

Exploitation vector: Network

Exploit availability: No

Vulnerable software:
GNU Bison
Other software / Other software solutions

Vendor: GNU

Description

The vulnerability allows a remote non-authenticated attacker to perform a denial of service (DoS) attack.

GNU Bison before 3.7.1 has a use-after-free in _obstack_free in lib/obstack.c (called from gram_lex) when a '�' byte is encountered. NOTE: there is a risk only if Bison is used with untrusted input, and the observed bug happens to cause unsafe behavior with a specific compiler/architecture. The bug report was intended to show that a crash may occur in Bison itself, not that a crash may occur in code that is generated by Bison.

Mitigation
Install update from vendor's website.

Vulnerable software versions

GNU Bison: 3.7

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External links
https://github.com/akimd/bison/commit/be95a4fe2951374676efc9454ffee8638faaf68d
https://github.com/akimd/bison/compare/v3.7...v3.7.1
https://lists.gnu.org/r/bug-bison/2020-07/msg00051.html

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Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.