Malicious client could set xattr value outside of BuildKit state directory
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 0.34.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.34.1.
- Exploitation?/40Exploitation: unknown (data gap). No CISA SSVC exploitation rating yet
- Exposure?/25Exposure: unknown (data gap). No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity4.5/10CVSS 4.5
- No patch0/5No signal
What would change the score
- Would score about 60 if added to CISA KEV
- Would score about 55 if CISA's SSVC rates exploitation active
- Would score about 27 if advisories confirm default setups are exposed
CVE-2026-121520 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.5 (medium) and affects BuildKit; fixed in 0.34.1.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 5/100 · provisional
- Fix
- Fixed in 0.34.1
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
BuildKit, the container image build engine, is affected by this vulnerability. A malicious client with access to its control APIs could set extended attributes on files outside BuildKit's state directory, potentially giving a program on the host elevated privileges.
Read the original description
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.
What to do
Upgrade to a fixed version: 0.34.1.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- Moby BuildKit
fixed in 0.34.1
Evidence 1
- Advisory
Corrections
None so far.
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Questions about CVE-2026-121520
Is CVE-2026-121520 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-121520?
BuildKit: before 0.34.1.Source: cve.now feed data
How do I fix CVE-2026-121520?
Upgrade to a fixed version: 0.34.1.Source: cve.now feed data