CVE-2021-33641

When processing files, malloc stores the data of the current line. When processing comments,...

7.8 HighFix available

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

Attack profile

How easy it is to exploit

Attack vector: Local
Complexity: Low
Privileges needed: None
User interaction: Required

What an attacker can affect

Confidentiality: High
Integrity: High
Availability: High

Exploit likelihood

0.28%Down 0.6 points since Jan 21, 2023

What each source reports

NVD Score used 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).

Record: CVE-2021-33641
CVSS 3.1: 7.8 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness: CWE-416
Updated: 2026-11-02

CVE List 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).

Record: CVE-2021-33641
CVSS 3.1: 7.8 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness: CWE-416
Updated: 2026-11-02

EUVDEUVD-2021-20318 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).

Record: EUVD-2021-20318
CVSS 3.1: 7.8 HighCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated: 2026-11-02

GitHub AdvisoriesGHSA-56c6-2pfc-9rvh 9.8

When processing files, malloc stores the data of the current line. When processing comments,...

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

Record: GHSA-56c6-2pfc-9rvh
CVSS 3.1: 9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-416
Updated: 2026-11-02

OSVOESA-2023-1033 5.5

byacc security update

Berkeley Yacc is an LALR(1) parser generator. Berkeley Yacc has been made as compatible as possible with AT&T Yacc. Berkeley Yacc can accept any input specification that conforms to the AT&T Yacc documentation. Specifications that take advantage of undocumented features of AT&T Yacc will probably be rejected.

Security Fix(es):

No description is available for this CVE.(CVE-2021-33641)

No description is available for this CVE.(CVE-2021-33642)

Record: OESA-2023-1033
CVSS 3.1: 5.5 MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated: 2026-11-02

OSVCLSA-2026-1782221814 No score

byacc: Fix of CVE-2021-33641

CVE-2021-33641: fix use-after-free in more_curly() in reader.c

Record: CLSA-2026-1782221814
Updated: 2026-11-02

Affected products

openeuler byacc

Affected packages

Affected packages
Package	Affected	Fixed
`byacc` TuxCare:AlmaLinux:9.2	before 2.0.20210109-4.el9.tuxcare.els1	2.0.20210109-4.el9.tuxcare.els1
`byacc` openEuler:20.03-LTS-SP1 From an advisory covering 2 CVEs	before 1.9.20200330-2.oe1	1.9.20200330-2.oe1
`byacc` openEuler:20.03-LTS-SP3 From an advisory covering 2 CVEs	before 1.9.20200330-2.oe1	1.9.20200330-2.oe1
`byacc` openEuler:22.03-LTS From an advisory covering 2 CVEs	before 2.0.20210808-4.oe2203sp1	2.0.20210808-4.oe2203sp1
`byacc` openEuler:22.03-LTS-SP1 From an advisory covering 2 CVEs	before 2.0.20210808-4.oe2203sp1	2.0.20210808-4.oe2203sp1

History

History
Recorded	Changed	Sources
Nov 6, 2026	affected, facts
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-33641 is a high vulnerability (CVSS 7.8) in Openeuler Byacc, published January 13, 2023. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.28%, the 20th percentile. Fixed in byacc 2.0.20210109-4.el9.tuxcare.els1.

Attack profile

How easy it is to exploit

What an attacker can affect

Exploit likelihood

What each source reports

Affected products

Affected packages

History

In short

References