Vulnerability · Published Jul 31, 2026 · Assigned by GitHub_M
CVE-2026-53501Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
High 8.2
In plain English
A high-severity security flaw in thumbor from thumbor. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 29% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:14 | thumbor | 7.8.0-1 | DEBIAN-CVE-2026-53501 |
| PyPI | thumbor | 7.8.0 | GHSA-mw3h-qjxj-6xg9 |
| PyPI | thumbor | 7.8.0 | PYSEC-2026-3620 |
| Ubuntu:26.04:LTS | thumbor | no fix listed | UBUNTU-CVE-2026-53501 |
Affected products (as reported)
Weakness: CWE-347 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
References
- https://github.com/thumbor/thumbor/security/advisories/GHSA-mw3h-qjxj-6xg9 x_refsource_CONFIRM
- https://github.com/thumbor/thumbor/commit/e3ae3e2500537b4d735df4144129a649374bb70b x_refsource_MISC
- https://github.com/thumbor/thumbor/releases/tag/7.8.0 x_refsource_MISC