CVE-2021-33641: When processing files, malloc stores the data of the current line

Routine

HIGH 7.8UPGRADE

CVE-2021-33641 is a high-severity flaw (CVSS 7.8) affecting byacc. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

When processing files, malloc stores the data of the current line. When processing comments, malloc incorrectly accesses the released memory (use after free).

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 81%)
CISA exploited list	No
Weakness	CWE-416
Published	2023-01-20
Last modified	2026-06-17

Publisher (CNA): openEuler · Vendor: openeuler

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

Am I affected?

Timeline

2023-01-20 21:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

openeuler byacc UPGRADE

Affected: < 1.9.20200330 · >= 2.0 and < 2.0.20210808

Fixed in: 1.9.20200330, 2.0.20210808

Safe to downgrade to: a release before 2.0

1. Check installed version

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

2. UPGRADE to 1.9.20200330 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade byacc

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade byacc

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.0 (Debian / Ubuntu)

apt-cache madison byacc sudo apt install byacc=<VERSION_BEFORE_2.0> sudo apt-mark hold byacc

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list byacc sudo dnf downgrade byacc-<VERSION_BEFORE_2.0> sudo dnf versionlock add byacc

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-2021-33641?

byacc: upgrade to 1.9.20200330, 2.0.20210808. Exact commands for each OS are on this page.

Is CVE-2021-33641 being exploited?

CVE-2021-33641 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-2021-33641 affect?

CVE-2021-33641 affects byacc. Severity is high (CVSS 7.8). When processing files, malloc stores the data of the current line. When processing comments, malloc incorrectly accesses the released memory (use after free).

How urgent is CVE-2021-33641?

Priority 32/100. High severity

Related CVEs

CVE-2021-33642 MEDIUM 5.5 UPGRADE When a file is processed, an infinite loop occurs in next_inline() of the more_curly() function.

References

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