CVE-2021-34123: An issue was discovered on atasm, version 1.09

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2021-34123 is a critical-severity flaw (CVSS 9.8) affecting atasm. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered on atasm, version 1.09. A stack-buffer-overflow vulnerability in function aprintf() in asm.c allows attackers to execute arbitrary code on the system via a crafted file.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-787
Published	2023-07-18
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: atasm project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-07-18 14:15 UTCPublished CVE record published
2026-06-17 03:55 UTCUpdated Record last modified

atasm project atasm DOWNGRADE

Affected: 1.09

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.09

1. Check installed version

apt-cache policy atasm || rpm -q atasm || atasm --version

2. No fixed release: DOWNGRADE to a release before 1.09 (Debian / Ubuntu)

apt-cache madison atasm sudo apt install atasm=<VERSION_BEFORE_1.09> sudo apt-mark hold atasm

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list atasm sudo dnf downgrade atasm-<VERSION_BEFORE_1.09> sudo dnf versionlock add atasm

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-34123?

atasm: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-34123 being exploited?

CVE-2021-34123 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-34123 affect?

CVE-2021-34123 affects atasm. Severity is critical (CVSS 9.8). An issue was discovered on atasm, version 1.09. A stack-buffer-overflow vulnerability in function aprintf() in asm.c allows attackers to execute arbitrary code on the system via a crafted file.

How urgent is CVE-2021-34123?

Priority 53/100. Critical severity; Remotely exploitable, no login, no user action

References

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