CVE-2026-53501

Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature

Published Jul 31, 2026 CVSS 3.1 · 8.2 High EPSS < 1% KEV · Not listed
Description
Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor’s HMAC validation can be bypassed due to the use of Python’s .replace() when removing the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation. This allows crafting URLs where the validated string differs from the actual requested resource, enabling loading images from unintended domains or paths. This issue is fixed in 7.8.0.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-mw3h-qjxj-6xg9 Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
History
Type Values Removed Values Added
First Time appeared Thumbor
Thumbor thumbor
Vendors & Products Thumbor
Thumbor thumbor
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor’s HMAC validation can be bypassed due to the use of Python’s .replace() when removing the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation. This allows crafting URLs where the validated string differs from the actual requested resource, enabling loading images from unintended domains or paths. This issue is fixed in 7.8.0.
Title Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
Weaknesses CWE-347
References
Metrics cvssV3_1

{'score': 8.2, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Jul 31, 2026, 7:58 PM
Reserved
Jun 9, 2026, 5:05 PM
Status
Deferred
Published
Jul 31, 2026, 7:17 PM
Modified
Sep 8, 2026, 8:51 PM