yasm v1.3.0 was discovered to contain a use after free via the function expand_mmac_params at /nasm/nasm-pp.c.

published 2023-05-09 3 y ago modified 2026-06-17 4 mo ago also EUVD-2023-36262

cvss: 7.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 24%
public exploits: 0; none known

yasm v1.3.0 was discovered to contain a use after free via the function expand_mmac_params at /nasm/nasm-pp.c. Note: Multiple third parties dispute this as a bug and not a vulnerability according to the YASM security policy.

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-31973 updated 2025-11-21 cvss 5.5

yasm: use-after-free in expand_mmac_params() in modules/preprocs/nasm/nasm-pp.c

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: total
Assessed: 2 y ago (2024-05-20)

Exploit prediction

0.31% chance of exploitation in the next 30 days, higher than 24% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/yasm/yasm/issues/207 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	7.8	CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD	3.1	5.5	CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
CNA	3.1	7.8	CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

tortall yasm

Classification

Weakness

CWE-401 Missing Release of Memory after Effective Lifetime
CWE-590 Free of Memory not on the Heap

References

github.com /yasm/yasm/issues/207
exploit, issue-tracking

Sources

CVE List CVE-2023-31973
NVD CVE-2023-31973

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary