EUVD-2026-58723
GHSA-4vqc-wpwg-vh7j
Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Primary rating from Vendor (https://github.com/siemens/kas) · only source for this CVE.
CVSS VectorVendor: https://github.com/siemens/kas
Lifecycle Timeline
3DescriptionCVE.org
Impact
So far, kas checks out and processes repositories regarding configuration includes prior to validating signatures of those repositories. This may allow to replace on original repository with one under the control of an attacker under very specific conditions.
First of all, the attacker must have gained control of a repository that a kas file of the victim is referencing. Furthermore, the following conditions must be fulfilled:
- the victim's kas configuration must include a configuration file from the attacked repository
- the repository state is referenced by tag, and no commit ID is specified (this is triggering a warning, though)
- the key used for validating the tag or commit signature is stored as file in a repository
- no fingerprint for the key is specified
- the
_source_dirkey must not be set by the victim when calling kas (e.g. by avoiding a local.config.yaml)
Given these conditions, the attacker could modify the included kas configuration in way that the key used to validate the tag signature of the attacker's repository could be replaced by an attacker-chosen key.
No other exploit possibilities have been identified so far, but this does not rule out that those may exist.
Patches
The vulnerability was introduced with a2480fe59b6421eb96cf3bd86527ae6e412a331e, commit https://github.com/siemens/kas/commit/5b2114becfc154b16ef496d24f8c2191a2297f57 is resolving this issue. A misuse of _source_dir is resolved by commit https://github.com/siemens/kas/commit/c443c0a1fd0f9bd6a689a44d95a252085fc6da88. Shadowing a commit by a branch of the same name is described in advisory https://github.com/siemens/kas/security/advisories/GHSA-qjwp-hrq6-r26r and is addressed by commit https://github.com/siemens/kas/commit/4cb4a3d01122ffaec9feaae768a5814092f6f9b5. All patches have been released along with kas version 5.3.
Workarounds
Pin the expected signature key via its fingerprint, also when storing it as file in a repository.
AnalysisAI
Late signature validation in Siemens kas (pip/kas >= 4.8, < 5.3) allows an attacker who has already compromised a referenced upstream repository to substitute the cryptographic key used to validate that repository's tag signatures, effectively bypassing integrity checks entirely. Because kas processes and applies configuration includes from external repositories before verifying their signatures, a malicious repository can redirect the signature-validation key to one under attacker control. No public exploit code has been identified at time of analysis, and exploitation requires a highly specific multi-condition scenario including prior supply-chain access to a referenced upstream repo. Vendor-released patch version 5.3 resolves all related attack vectors.
Technical ContextAI
kas is a Siemens-maintained Python tool (pip/kas) for managing Yocto/OpenEmbedded build environment configurations, typically used in embedded Linux workflows. It supports multi-repository builds by fetching and composing configuration from referenced Git repositories. The root cause is CWE-347 (Improper Verification of Cryptographic Signature): kas performs Git checkout and configuration parsing of included repositories prior to validating their cryptographic signatures. This ordering flaw means that attacker-controlled content from an upstream repository is parsed and applied - including key file paths - before any trust assertion is made. A secondary issue (addressed by the GHSA-qjwp-hrq6-r26r advisory) involves branch names shadowing commit refs: when a repository is pinned by tag rather than full commit hash, git checkout could silently resolve to a branch of the same name as the tag. The patch (commit 4cb4a3d) guards against this by appending '^{commit}' to any 40/64-character hex ref, ensuring only actual commit objects are resolved.
RemediationAI
The primary remediation is to upgrade to kas version 5.3, which includes all three patches: commit 5b2114b (late validation ordering fix), commit c443c0a (misuse of _source_dir), and commit 4cb4a3d (branch-shadowing commit disambiguation). Upgrade via pip: 'pip install --upgrade kas>=5.3'. If an immediate upgrade is not feasible, the vendor-documented workaround is to pin the expected signature key via its fingerprint rather than relying on a key file stored inside a repository - this breaks the attacker's ability to substitute the key even if they control the upstream repo. Additionally, operators should pin all repository references to explicit commit hashes rather than tags, which both eliminates the tag-shadowing vector and triggers kas's existing warning mechanism when tags are used without commit IDs. Advisory references: https://github.com/siemens/kas/security/advisories/GHSA-4vqc-wpwg-vh7j and https://github.com/siemens/kas/security/advisories/GHSA-qjwp-hrq6-r26r.
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