What is CVE-2018-20538?

CVE-2018-20538 is a medium-severity vulnerability in Nasm Netwide Assembler, classified under Use After Free. CVSS score: 5.5/10. Published 2018-12-28.

How severe is CVE-2018-20538?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Is CVE-2018-20538 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Use After Free in Nasm Netwide Assembler

CVE-2018-20538

There is a use-after-free at asm/preproc.c (function pp_getline) in Netwide Assembler (NASM) 2.14rc16 that will cause a denial of service during certain finishes tests.

Vulnerability class: Use-After-Free

Published 2018-12-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.008 (54.6th percentile), scored 2026-10-02.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 54.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Nasm Netwide Assembler — versions 2.14.0

Weakness classification (CWE)

CWE-416 — Use After Free

Public proof-of-concept exploits

References

bugzilla.nasm.us/show_bug.cgi (Exploit, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2018-20538?: CVE-2018-20538 is a medium-severity vulnerability in Nasm Netwide Assembler, classified under Use After Free. CVSS score: 5.5/10. Published 2018-12-28.
How severe is CVE-2018-20538?: Medium severity. CVSS v3 base score is 5.5 out of 10.
Is CVE-2018-20538 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.