---
title: "CVE-2026-109391: Square Squash - Insecure Deserialization"
description: "Square Squash contains an insecure deserialization vulnerability caused by unsafe YAML.load usage in the /api/1.0/symbolication endpoint, letting unauthenticated attackers execute arbitrary code remotely, exploit requires crafted YAML payload."
url: https://panop.io/threat-heartbeat/CVE-2026-109391/
---

# CVE-2026-109391 Square Squash - Insecure Deserialization

Square Squash contains an insecure deserialization vulnerability caused by unsafe YAML.load usage in the /api/1.0/symbolication endpoint, letting unauthenticated attackers execute arbitrary code remotely, exploit requires crafted YAML payload.

CVSS base score 8.1 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.48% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-109391)

## Details

Type

Insecure Deserialization

Impact

Remote Code Execution

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Published

12 October 2026

Updated

15 October 2026

Weakness

[CWE-502](https://cwe.mitre.org/data/definitions/502.html)

## Vendor fix

Update to the latest version with the deserialization fix applied.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-109391](https://nvd.nist.gov/vuln/detail/CVE-2026-109391)
- [https://github.com/SquareSquash/web](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/controllers/api/v1_controller.rb)
- [https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/app/models/symbolication.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/config/preinitializers/safe_yaml.rb)
- [https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/lib/workers/symbolication\_creator.rb](https://github.com/SquareSquash/web/blob/e73f2805f9eb30780a5c213b001f0f4255660fbf/lib/workers/symbolication_creator.rb)
- [https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/HJ87QX5ifg](https://hackmd.io/@1ExmmukzRMWN7B4gQ4W-4Q/HJ87QX5ifg)
- [https://www.vulncheck.com/advisories/square-squash-through-commit-e73f280-unauthenticated-yaml-deserialization-via-symbolication-api](https://www.vulncheck.com/advisories/square-squash-through-commit-e73f280-unauthenticated-yaml-deserialization-via-symbolication-api)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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