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Vulnerabilities CVE-2026-53501

CVE-2026-53501

High
Open
TLP:CLEAR

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

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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.

Details

CVSS Score
8.2
EPSS Score
0.21%

11.3th percentile

CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
Confidence
90%
Published
Jul 31, 2026
Last Modified
Jul 31, 2026
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