CVE-2026-53500 Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypass via wildcard dot
Attackers can bypass hostname allowlists in Thumbor by exploiting unescaped regex patterns in ALLOWED_SOURCES, enabling unauthorized server-side requests.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53500?
CVE-2026-53500 is a high-severity server-side request forgery 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, the ALLOWED_SOURCES configuration passes plain strings to re.match() without escaping dots, so a hostname differing at dot positions can match the allowlist. This issue is fixed in 7.8.0.
Weakness: CWE-918
Which versions are affected by CVE-2026-53500?
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-2026-53500?
Upgrade thumbor to 7.8.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-53500 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53500 exists.
Sources
Also known as DEBIAN-CVE-2026-53500, GHSA-6x26-6r6f-m537, PYSEC-2026-3617, UBUNTU-CVE-2026-53500.