CVE-2026-53505 Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS
An attacker can cause denial of service in Thumbor by triggering unbounded resizes via the proportion filter, exhausting CPU and memory resources.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53505?
CVE-2026-53505 is a high-severity denial of service 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 filters:proportion(<value>) filter does not enforce an upper bound on <value> and runs in the post-transform phase. An attacker can trigger extremely large resizes (CPU/memory exhaustion) and cause denial of service. This issue is fixed in 7.8.0.
Weakness: CWE-400
Which versions are affected by CVE-2026-53505?
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-2026-53505?
Upgrade thumbor to 7.8.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-53505 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-53505 exists.
Sources
Also known as DEBIAN-CVE-2026-53505, GHSA-phj3-59pf-cp83, PYSEC-2026-3621, UBUNTU-CVE-2026-53505.