Security readout for executives and security teams
Plain-English summary
CVE-2021-33641 is a high-severity memory safety flaw in byacc. A user must process a malicious or malformed file, so this is mainly a risk to developer workstations, build systems, and packaging pipelines rather than public web services.
Executive priority
Treat this as a build and developer environment hardening priority. It is not described as remotely exploitable over the network, but compromised build hosts can create serious downstream security and supply-chain risk.
Technical view
The issue is a CWE-416 use-after-free while byacc processes comments in files. The CVSS 3.1 score is 7.8 with local attack vector, low complexity, no privileges required, user interaction required, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most likely where affected byacc versions process files from contributors, third parties, generated sources, or untrusted repositories. The affected product is byacc before 1.9.20200330 and before 2.0.20210808.
Exploitation context
The provided sources do not report active exploitation, and the CVE is not listed as KEV. Exploitation requires local file processing and user interaction, but successful memory corruption could materially affect the host running byacc.
Researcher notes
Evidence is limited to the CVE record, affected version ranges, CVSS vector, CWE classification, and a referenced openEuler byacc commit. No public source in the bundle confirms exploit availability or detailed remediation beyond version boundaries.
Mitigation direction
- Inventory byacc installations on developer, CI, and packaging systems.
- Upgrade byacc to 1.9.20200330, 2.0.20210808, or later where available.
- Check operating system or distribution advisories for packaged fixes.
- Restrict byacc processing of untrusted files until fixed.
- Rebuild affected build images after package updates.
Validation and detection
- Check installed byacc versions against the affected version ranges.
- Review CI jobs and build scripts for byacc usage.
- Identify repositories or workflows that process external grammar files.
- Confirm vendor or distribution package changelogs include the fix.
- Verify updated build images no longer contain affected byacc versions.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-33641 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source materials
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.