# CVE-2026-53504: Thumbor ReDoS in convolution filter

Source: https://junglewise.ai/threats/cve-2026-53504-thumbor-redos-in-convolution-filter  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-31. Updated: 2026-07-31  
License: CC BY 4.0 with a link back

CVE-2026-53504 · Severity: high · CVSS 7.5 · Published 2026-07-31

Thumbor is an open-source service used to resize and process images on the fly. A flaw in how it handles certain image filters allows an attacker to send a specially crafted web request that freezes the service. This can lead to a total service outage, preventing legitimate users from viewing or processing images.

Technologies: [thumbor (PyPI)](https://junglewise.ai/threats/technologies/thumbor). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-53504 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-53504 being exploited in the wild.

**How severe is CVE-2026-53504?** High severity, with a CVSS score of 7.5, published 31 July 2026.

**Which products and versions are affected?** thumbor (PyPI) <= 7.7.7, ECOSYSTEM:introduced=0,fixed=7.8.0.

**Is there a fix for CVE-2026-53504?** Yes. thumbor (PyPI): upgrade to 7.8.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-53504 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-53504?** Check whether you run thumbor (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- thumbor (PyPI): upgrade to 7.8.0 or later

  ```sh
  pip install "thumbor>=7.8.0"
  ```


## Technical details

A Regular Expression Denial of Service (ReDoS) vulnerability exists in the convolution filter of Thumbor. The root cause is an inefficient regular expression used to parse filter parameters, specifically a subpattern that behaves like (\d+)*,\d+, which triggers exponential backtracking when processing long strings of repeated numeric input. An unauthenticated remote attacker can exploit this by sending a crafted URL containing a malformed convolution filter string. This causes the Python interpreter to exhaust CPU resources while attempting to match the expression, leading to a denial of service for the image processing worker. The issue is resolved in version 7.8.0 by replacing the ambiguous regex with a non-backtracking alternative.

## Affected products

- thumbor thumbor < 7.8.0

## Identifiers

- CVE-2026-53504
- GHSA-5vjc-7cxw-4w6j
- PYSEC-2026-3616

## Timeline

- 2026-05-30: patched: Version 7.8.0 released
- 2026-06-10: advisory: GitHub Security Advisory published
- 2026-07-31: disclosed: CVE published to NVD

## References

- [https://github.com/thumbor/thumbor/commit/3f38fe1610d20168e91f76d432212de30727eb2e](https://github.com/thumbor/thumbor/commit/3f38fe1610d20168e91f76d432212de30727eb2e)
- [https://github.com/thumbor/thumbor/releases/tag/7.8.0](https://github.com/thumbor/thumbor/releases/tag/7.8.0)
- [https://github.com/thumbor/thumbor/security/advisories/GHSA-5vjc-7cxw-4w6j](https://github.com/thumbor/thumbor/security/advisories/GHSA-5vjc-7cxw-4w6j)

## Related threats

- [Thumbor uncontrolled resource consumption in proportion filter](https://junglewise.ai/threats/cve-2026-53505-thumbor-uncontrolled-resource-consumption-in-proportion-filter)
- [Thumbor divide by zero in convolution filter C extension](https://junglewise.ai/threats/cve-2026-53503-thumbor-divide-by-zero-in-convolution-filter-c-extension)
- [Thumbor path traversal in file_loader via encoded path segments](https://junglewise.ai/threats/cve-2026-53502-thumbor-path-traversal-in-file-loader-via-encoded-path-segments)
- [Thumbor HMAC validation bypass via multiple signature injection](https://junglewise.ai/threats/cve-2026-53501-thumbor-hmac-validation-bypass-via-multiple-signature-injection)
- [Thumbor SSRF via unescaped dots in ALLOWED_SOURCES](https://junglewise.ai/threats/cve-2026-53500-thumbor-ssrf-via-unescaped-dots-in-allowed-sources)