Executive brief
Siemens kas is a tool used to set up and build complex software projects by managing multiple source code repositories. A vulnerability exists where the tool can be tricked into downloading a malicious version of source code if an attacker creates a branch name that looks like a specific version identifier (a git commit hash). This could allow an attacker who has compromised a source repository to execute a supply-chain attack by providing unauthorized code instead of the expected version.
Technical details
A vulnerability in Siemens kas (prior to version 5.3) allows for the substitution of a git commit with a branch of the same name. When kas performs a checkout using a commit ID (SHA-1 or SHA-256) for integrity validation, it does not explicitly force the reference to be treated as a commit object. An attacker who has gained control over a referenced repository can create a branch named with the hex string of a valid commit hash. Because git checkout prioritizes or accepts branch names that match the hash string, kas may check out the head of the malicious branch instead of the specific immutable commit. This issue is mitigated by appending '^{commit}' to the reference during checkout to ensure only commit objects are resolved.
Affected products
- Siemens kas < 5.3
Timeline
- 2026-05-27: disclosed: Initial publication by Siemens
- 2026-06-01: advisory: GitHub Advisory published
- 2026-06-01: patched: Released in version 5.3