CVE-2026-53501 Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
Attackers can bypass HMAC validation in Thumbor by manipulating URL signatures, allowing unauthorized access to images from unintended domains or paths.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53501?
CVE-2026-53501 is a high-severity vulnerability in thumbor, published on 31 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-347
Which versions are affected by CVE-2026-53501?
3 open source packages ship an affected version, including thumbor.
| Package | Affected | Fixed in |
|---|---|---|
thumbor PyPI | All versions | 7.8.0 |
thumbor PyPI | All versions | 7.8.0 |
thumbor PyPI | All versions | 7.8.0 |
How do I fix CVE-2026-53501?
Upgrade thumbor to 7.8.0 or later.
Is CVE-2026-53501 being exploited?
There is no known exploitation of CVE-2026-53501 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-53501, GHSA-mw3h-qjxj-6xg9, PYSEC-2026-3620, UBUNTU-CVE-2026-53501.