Siemens kas CVE-2026-47191

Exploitation requires two concurrent conditions: (1) the attacker must have write access to a git repository that is referenced by a kas configuration file in the target environment - this implies either compromise of the upstream repository, repository takeover (e.g., abandoned GitHub org), or a trusted-insider scenario; and (2) the kas configuration must reference that repository using a commit SHA (either 40-character SHA-1 or 64-character SHA-256). SHA-256 commit IDs are primarily at risk because creating a branch with a SHA-256-matching name is feasible, while SHA-1 collision-based substitution is separately limited by computational cost. The vulnerability does not affect configurations that reference repositories by branch or tag name rather than commit SHA, since those carry no expectation of commit-level integrity anyway. Local-only repositories or repositories hosted exclusively in environments the defender controls are not exploitable.

No CVSS score or vector was provided for this CVE, preventing quantitative scoring. Risk must be assessed qualitatively from available signals. The attack requires an adversary to have write access to an external git repository that is already trusted and referenced in a kas configuration - a meaningful prerequisite that limits opportunistic exploitation. However, for supply-chain scenarios (compromised upstream repos, typosquatting, repository takeovers on platforms like GitHub), this is a realistic threat model. The vulnerability directly undermines a core security assumption of reproducible build systems: that pinning a commit SHA guarantees what code is fetched. The impact on SHA-256 commits is particularly significant because users may treat SHA-256 pins as cryptographically strong guarantees. SHA-1 collision attacks remain computationally expensive and are a separate, harder threat vector. No EPSS score, KEV listing, or public POC is available, suggesting limited or no observed exploitation to date. Despite the lack of a CVSS score, this is a meaningful supply-chain integrity risk for any organization using kas to manage external dependencies in Yocto builds.

An attacker who has gained write access to an upstream git repository referenced in a target organization's kas configuration (through repository takeover, credential compromise, or a malicious contributor scenario) creates a new branch whose name is the exact 64-character SHA-256 hex string of the commit pinned in the kas config. The branch points to attacker-controlled code. When a developer or CI system runs kas to set up the Yocto build workspace, kas invokes git checkout <sha> without the ^{commit} disambiguation suffix, causing git to resolve the branch rather than the pinned commit, and the malicious code is silently introduced into the build environment.