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Vulnerability record · CVE-2026-109391 · published 12 October 2026

CVE-2026-109391: Deserialization of untrusted data vulnerability

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.

9.2 CVSS 4.0 Critical EPSS 0.48% · top 60.4% CWE-502 · Deserialization of untrusted data Received
9.2CVSS 4.0 base score
0.48%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
7References
13 Oct 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/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:

References

LinkTags
https://github.com/SquareSquash/web
https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/app/controllers/api/v1_controller.rb
https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/app/models/symbolication.rb
https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/config/preinitializers/safe_yaml.rb
https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/lib/workers/symbolication_creator.rb
https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/HJ87QX5ifg
https://www.vulncheck.com/advisories/square-squash-through-commit-e73f280-unauthenticated-yaml-deserialization-via-symbo

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Source: NIST National Vulnerability Database (record CVE-2026-109391), CISA KEV, FIRST EPSS (scores of 2026-10-14). This page is refreshed as NVD updates the record.