Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypass via wildcard dot

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-53500: 0.50% estimated exploitation activity in the next 30 days; percentile 42.75 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The ALLOWEDSOURCES configuration is meant to restrict which hosts Thumbor's HTTP loader may fetch images from. Plain-string entries in that list (the overwhelming majority of real-world and documented configurations) are passed directly to re.match() without escaping. Because . is a regex wildcard, every dot in a domain name becomes a bypass vector: s.glbimg.com silently matches sXglbimgYcom, sAglbimg.com, and any other hostname that differs only at a dot position. This undermines the primary SSRF defence that ALLOWEDSOURCES is intended to provide. Affected component thumbor/loaders/httploader.py — validate() Proof of concept Root cause thumbor/loaders/httploader.py (before fix): Impact An attacker who can influence the image source URL passed to Thumbor can fetch images from arbitrary hosts, bypassing the ALLOWEDSOURCES allowlist. Preconditions: - ALLOWEDSOURCES contains at least one plain-string entry (the common case; all official documentation examples use plain strings).…

Published by the source

31 Jul 2026, 18:36 UTC

Last modified by the source

30 Sep 2026, 18:44 UTC

Source last checked

26 Oct 2026, 13:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6x26-6r6f-m537

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# Patch Next advisory brief: CVE-2026-53500

Advisory: Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypass via wildcard dot
IDs: CVE-2026-53500, GHSA-6x26-6r6f-m537
Record: https://patchnext.com/advisories/cve-2026-53500 (revision 1, source checked 26 Oct 2026, 13:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: thumbor 7.8.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI thumbor: affected <= 7.7.7; fixed in 7.8.0

## Suggested inspection (read-only)
- `python -m pip show thumbor`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on thumbor.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6x26-6r6f-m537 (GitHub-reviewed advisory GHSA-6x26-6r6f-m537 lists affected ranges: PyPI thumbor >=0 <=7.7.7)

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