CVE-2026-53504: Thumbor Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-5vjc-7cxw-4w6j
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CVSS 7.5
CWE-400
Published
Advisory Summary

CVE-2026-53504 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Thumbor libraries in the PyPI ecosystem. The issue involves thumbor has regex denial of service (redos) in `convolution` filter. Remediation is available by upgrading affected packages to version 7.8.0.

CVE-2026-53504 at a Glance

CVE Identifier CVE-2026-53504
GHSA Identifier GHSA-5vjc-7cxw-4w6j
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-400: Uncontrolled Resource Consumption
Affected Product Thumbor
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-53504

To remediate this vulnerability, upgrade all affected Thumbor dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

thumbor fixed: 7.8.0 
pip install thumbor>=7.8.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show thumbor

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-53504, inspect your installed packages using pip:

pip show thumbor

Analyze the terminal output to locate any version of Thumbor in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 7.8.0), your application is affected.

Note: The pip show thumbor command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Thumbor, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary The regular expression used to parse the `convolution` filter exhibits exponential-time backtracking for certain inputs, enabling a Regular Expression Denial of Service (ReDoS). ### Details The RegExp for `convolution` is defined as `convolution\((?:\s*((?:[-]?[\d]+\.?[\d]*[;])*(?:[-]?[\d]+\.?[\d]*))\s*)(?:,\s*([\d]+)\s*)(?:,\s*([Tt]rue|[Ff]alse|1|0)\s*)?\)`. Within this expression a dangerous subpattern effectively behaves like `(\d+)*,\d+`. ### PoC A filter string containing many repeated values will exhaust `re.match`: - `convolution(-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11)` - http://localhost:8888/unsafe/0x0/smart/filters:convolution(-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11)/x.png The evaluation occurs on https://github.com/thumbor/thumbor/blob/master/thumbor/filters/__init__.py#L189. ### Impact A specially crafted URL will lead to denial of service, as new images won't be processed until `re.match` returns.

CVE-2026-53504 Affected Thumbor Versions

1 component(s)
Fixed Versions:
7.8.0
Product / Package Ecosystem Affected Versions Fixed Version
thumbor
pypi/thumbor
PyPI
< 7.8.0
7.8.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/thumbor/thumbor/security/advisories/GHSA-5vjc-7cxw-4w6j
Security Fix Commit FIX COMMIT
https://github.com/thumbor/thumbor/commit/3f38fe1610d20168e91f76d432212de30727eb2e
Thumbor Source Repository REPOSITORY
https://github.com/thumbor/thumbor
Thumbor Release RELEASE
https://github.com/thumbor/thumbor/releases/tag/7.8.0

Frequently Asked Questions

What is CVE-2026-53504?
CVE-2026-53504 is a security vulnerability in Thumbor involving Thumbor has Regex Denial of Service (ReDoS) in `convolution` filter under CWE-400: Uncontrolled Resource Consumption.
Which Thumbor versions are affected?
Affected versions include releases prior to 7.8.0 across affected packages: thumbor.
What version fixes CVE-2026-53504?
Upgrading to 7.8.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is thumbor affected?
Yes, thumbor is affected in releases prior to 7.8.0. Upgrade your dependency to 7.8.0 or later.
What is the CVSS score of CVE-2026-53504?
CVE-2026-53504 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-53504?
CVE-2026-53504 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).
How can I check PyPI dependencies for CVE-2026-53504?
Run the dependency tree command: 'pip show thumbor'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5vjc-7cxw-4w6j",
  "modified" : "2026-07-31T18:58:28Z",
  "published" : "2026-07-31T18:58:28Z",
  "aliases" : [ "CVE-2026-53504" ],
  "summary" : "Thumbor has Regex Denial of Service (ReDoS) in `convolution` filter",
  "details" : "### Summary\nThe regular expression used to parse the `convolution` filter exhibits exponential-time backtracking for certain inputs, enabling a Regular Expression Denial of Service (ReDoS).\n\n### Details\nThe RegExp for `convolution` is defined as `convolution\\((?:\\s*((?:[-]?[\\d]+\\.?[\\d]*[;])*(?:[-]?[\\d]+\\.?[\\d]*))\\s*)(?:,\\s*([\\d]+)\\s*)(?:,\\s*([Tt]rue|[Ff]alse|1|0)\\s*)?\\)`. Within this expression a dangerous subpattern effectively behaves like `(\\d+)*,\\d+`.\n\n### PoC\nA filter string containing many repeated values will exhaust `re.match`:\n- `convolution(-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11)`\n- http://localhost:8888/unsafe/0x0/smart/filters:convolution(-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11;-11)/x.png\n\nThe evaluation occurs on https://github.com/thumbor/thumbor/blob/master/thumbor/filters/__init__.py#L189.\n\n### Impact\nA specially crafted URL will lead to denial of service, as new images won't be processed until `re.match` returns.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "thumbor"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "7.8.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 7.7.7"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/thumbor/thumbor/security/advisories/GHSA-5vjc-7cxw-4w6j"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thumbor/thumbor/commit/3f38fe1610d20168e91f76d432212de30727eb2e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/thumbor/thumbor"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/thumbor/thumbor/releases/tag/7.8.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-31T18:58:28Z",
    "nvd_published_at" : null
  }
}