CVE-2026-109391 Square Squash through commit e73f280 Unauthenticated YAML Deserialization via Symbolication API
Unauthenticated attackers can achieve remote code execution in Square Squash by submitting malicious YAML payloads to the symbolication API.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-109391?
CVE-2026-109391 is a critical unsafe deserialization vulnerability in Square Squash, published on 12 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Square Squash through commit e73f280 contains an insecure deserialization vulnerability that allows unauthenticated attackers to store crafted YAML via the POST /api/1.0/symbolication endpoint. When occurrences referencing the attacker-controlled symbolication UUID are symbolicated, the stored values are passed to YAML.load with SafeYAML in unsafe mode, enabling arbitrary Ruby object deserialization and potential code execution.
Weakness: CWE-502
Which versions are affected by CVE-2026-109391?
How do I fix CVE-2026-109391?
No fix has been published for CVE-2026-109391 yet. Limit exposure of the affected software until one is available.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-109391 being exploited?
There is no known exploitation of CVE-2026-109391 in the wild and no public exploit code.
Sources
Also known as GHSA-f7j3-hchq-qp35.