Security readout for executives and security teams
Plain-English summary
CVE-2021-33642 is a denial-of-service issue in byacc. Processing a crafted or problematic file can trigger an infinite loop, consuming availability. The CVSS score is 5.5 because exploitation is local and requires user interaction, but successful triggering can have high availability impact.
Executive priority
Treat as a moderate operational risk. It is unlikely to be internet-exploitable directly, but it can disrupt build or developer workflows if untrusted inputs reach byacc.
Technical view
The issue is CWE-835: an infinite loop in next_inline() within more_curly() during file processing. The CVE record lists affected byacc versions as below 1.9.20200330 and below 2.0.20210808. The provided sources do not describe confidentiality or integrity impact.
Likely exposure
Exposure is most likely on developer workstations, CI systems, build containers, or packaging environments that run byacc against files from external contributors, source packages, or automated build inputs.
Exploitation context
The CVSS vector is local, low complexity, no privileges required, and user interaction required. The source bundle does not show CISA KEV listing or any cited evidence of active exploitation.
Researcher notes
Evidence is sparse in the provided bundle. The affected function and CWE indicate denial of service through non-terminating parsing behavior, but the sources do not provide detailed root cause, exploit status, or comprehensive remediation instructions.
Mitigation direction
- Identify all byacc installations in developer, CI, and build environments.
- Update byacc using trusted vendor or distribution guidance.
- Restrict automated processing of untrusted grammar files where feasible.
- Apply the referenced distribution fix if it matches your package source.
- Monitor vendor advisories for corrected package versions and backports.
Validation and detection
- Confirm installed byacc versions are not in the affected ranges.
- Review CI and build jobs that process externally supplied parser files.
- Check package advisories for the exact distribution build in use.
- Test representative parser builds after updating byacc.
- Document any remaining untrusted-file processing risk.
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-835: 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-2021-33642 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N/I:N/A:H1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/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.
Loop with Unreachable Exit Condition ('Infinite Loop')
Loop with Unreachable Exit Condition ('Infinite Loop') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.