Security readout for executives and security teams
Plain-English summary
Certain GitLab Runner versions could mix CI job log output between jobs. The main business risk is confidentiality: sensitive build output, tokens, or operational details printed by one job might appear where another job’s trace is visible.
Executive priority
Treat as a moderate confidentiality issue. Prioritize shared runners, sensitive build pipelines, and environments where many teams or projects use the same runner fleet.
Technical view
The issue involves trace file buffers in GitLab Runner reusing file descriptor 0 for multiple traces under specific circumstances, causing output from several jobs to mix. CVSS 3.1 is 5.3 with high confidentiality impact, high attack complexity, and low privileges required.
Likely exposure
Exposure is limited to organizations running affected GitLab Runner versions: below 14.3.4, 14.4 before 14.4.2, or 14.5 before 14.5.2.
Exploitation context
The provided sources do not show active exploitation, and this CVE is not marked KEV. Exploitation appears constrained by high complexity and requires low privileges, but successful abuse could expose sensitive CI trace output.
Researcher notes
Evidence is limited to the CVE record and GitLab references. The sources describe log trace mixing, not code execution or integrity impact. Validate runner versions and trace visibility before assigning emergency response priority.
Mitigation direction
- Upgrade GitLab Runner outside the affected version ranges.
- Review GitLab’s advisory and runner issue for exact vendor guidance.
- Reduce secrets printed in CI logs and job output.
- Restrict access to CI job traces to necessary users only.
Validation and detection
- Inventory all GitLab Runner versions across shared and project-specific runners.
- Confirm no runner remains in the affected version ranges.
- Review CI trace logs for unexpected mixed job output.
- Check CI jobs for secrets or sensitive data written to logs.
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.
CVE-2021-39947 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
- 5.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
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:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N1.63.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://gitlab.com/gitlab-org/gitlab-runner/-/issues/28732CVE reference · x_refsource_MISC
- https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39947.jsonCVE reference · x_refsource_CONFIRM
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.