What’s Vulnerable › Vulnerabilities

CVE-2026-53501: Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature

• Severity: high (CVSS 8.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-31 · updated 2026-09-08
• Weakness: CWE-347

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.

Affected products

• thumbor: before 7.8.0

References

• 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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