CVE-2020-21686

Exp

A stack-use-after-scope issue discovered in expand_mmac_params function in preproc.c in nasm before 2.15.04 allows remote attackers to cause a denial of service via crafted asm file.

Published: 2023-08-22 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-21686 is rated Exploit Available (50.9/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.18%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2020-21686

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2020-21686

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-11-21 0.09% 0.18% +0.09%
2 2025-11-18 0.18% 0.09% -0.09%
3 2025-09-16 — 0.18% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-21686

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]

Weakness enumeration for CVE-2020-21686

OS Trackers for CVE-2020-21686

vendor priority summary link
debian not yet assigned CVE-2020-21686 not yet assigned priority: Debian including 1 source packages (nasm), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2020-21686
redhat low — https://access.redhat.com/security/cve/CVE-2020-21686
suse low CVE-2020-21686 severity low: SUSE including 1 source package names (nasm), 17 product×package rows across 17 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 7.1, … (17 product lines)): Will Not Fix 16, Known Not Affected 1. https://www.suse.com/security/cve/CVE-2020-21686/
ubuntu medium CVE-2020-21686 medium priority: Ubuntu including 1 source packages (nasm), 12 status rows across 12 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 4, needs-triage 4, not-affected 4. https://ubuntu.com/security/CVE-2020-21686

Affected software / configurations for CVE-2020-21686

Vendor Product Version Raw CPE
nasm netwide_assembler < 2.15.04 cpe:2.3:a:nasm:netwide_assembler:*:*:*:*:*:*:*:*

References for CVE-2020-21686

URL Tags
https://bugzilla.nasm.us/show_bug.cgi?id=3392643 Exploit Issue Tracking Vendor Advisory
cvelogic Threat Intelligence