Deserialization in Square Squash
CVE-2026-109391
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.
Vulnerability class: Insecure Deserialization
Published .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/HJ87QX5ifg (technical-description, exploit)
- github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/app/c… (technical-description)
- github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/confi… (technical-description)
- github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/lib/w… (technical-description)
- github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/app/m… (technical-description)
- github.com/SquareSquash/web (product)
- www.vulncheck.com/advisories/square-squash-through-commit-e73f280-unauthenticat… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-109391?
- CVE-2026-109391 is a high-severity vulnerability in Square Squash, classified under Deserialization of Untrusted Data. CVSS score: 8.1/10. Published 2026-10-12.
- How severe is CVE-2026-109391?
- High severity. CVSS v3 base score is 8.1 out of 10.