Use after free in byacc
Priority LOW 34CWE-416Published · Updated
Key facts
- Attack vector
- Local
- Privileges required
- None
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Will not fix Red Hat: no fix planned
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and Red Hat. Impact type from CWE-416 and the CVSS impact.
Summary
When processing files, malloc stores the data of the current line. When processing comments, malloc incorrectly accesses the released memory (use after free).
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00278 20th percentileScored 2026-11-07
Fix Will not fix Red Hat: no fix planned
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | byacc | <1.9.20200330 and <2.0.20210808 | — | No fix listed | CNA |
- byacc Vendor— Affected <1.9.20200330 and <2.0.20210808 Fixed in — No fix listed CNA
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 7 | Affected | No fix planned: Will not fix |
Not affected: 2 products
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
Timeline
- 2026-10-02 Threatist record created from CVE-2021-33641
- 2026-10-03 Alias added: GHSA-56c6-2pfc-9rvh
References
More openEuler Byacc vulnerabilities
- TI-2021-13016 When a file is processed, an infinite loop occurs in next_inline() of the more_curly() function. CVSS 3.1MEDIUM 5.5
Sources
- CVE-2021-33641 · CVE Program
- CVE-2021-33641 · NVD
- FIRST EPSS
- GHSA-56c6-2pfc-9rvh · GitHub Advisory Database · CC BY 4.0
- CVE-2021-33641 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences