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Vulnerability record · CVE-2026-53501 · published 31 July 2026

CVE-2026-53501: Improper verification of cryptographic signature vulnerability

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.

8.2 CVSS 3.1 High EPSS 0.35% · top 73.7% CWE-347 · Improper verification of cryptographic signature Deferred
8.2CVSS 3.1 base score
0.35%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
3References
8 Sep 2026Last modified by NVD

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.

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

References

LinkTags
https://github.com/thumbor/thumbor/commit/e3ae3e2500537b4d735df4144129a649374bb70b
https://github.com/thumbor/thumbor/releases/tag/7.8.0
https://github.com/thumbor/thumbor/security/advisories/GHSA-mw3h-qjxj-6xg9

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Source: NIST National Vulnerability Database (record CVE-2026-53501), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.