CVE-2026-53501
Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
CVSS Score
8.2
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-347 |
| Vendor | thumbor |
| Product | thumbor |
| Published | Jul 31, 2026 |
| Last Updated | Jul 31, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
Low
Affected Versions
thumbor / thumbor
< 7.8.0