CVSS 4.0
4.5 mediumCVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:HCVE-2026-121520
Medium (4.5). EPSS 0.1% estimated probability of exploitation activity in the next 30 days.
In BuildKit versions prior to v0.34.1, a malicious client with access to the BuildKit control APIs can submit a build request that sets an extended attribute on a file outside the BuildKit state directory. Extended attributes in the trusted. or security. namespaces may also be set, potentially giving a program on the host elevated privileges. This issue affects build services that accept build requests from untrusted users. The issue is fixed in v0.34.1.
Severity
- EPSS
- 0.1% estimated probability of exploitation activity in the next 30 days; 3rd percentile. Scored 2026-11-04. A forecast for this CVE across the internet, not for your own systems.
- CWE
- CWE-61 UNIX Symbolic Link (Symlink) Following
- OWASP Top 10
- A01:2025 Broken Access Control
- Published
- Record from
- the NVD, synced
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Explain CVE-2026-121520 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-121520?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-121520?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-121520 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| Moby BuildKit | before 0.34.1 |
Attack patterns (CAPEC)
- CAPEC-27 Leveraging Race Conditions via Symbolic Links Likelihood: Medium · Severity: High
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.