Vulnerability-Lookup

CVE-2026-53505 (GCVE-0-2026-53505)

Vulnerability from cvelistv5 – Published: 2026-07-31 19:00 – Updated: 2026-08-03 17:20

Title

Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS

Summary

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.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

GitHub_M

References

3 references

URL	Tags
https://github.com/thumbor/thumbor/security/advis…	x_refsource_CONFIRM
https://github.com/thumbor/thumbor/commit/2c71611…	x_refsource_MISC
https://github.com/thumbor/thumbor/releases/tag/7.8.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
thumbor	thumbor	Affected: < 7.8.0

Show details on NVD website

JSON

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GHSA-PHJ3-59PF-CP83

Vulnerability from github – Published: 2026-07-31 19:00 – Updated: 2026-07-31 19:00

Summary

Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS

Details

Summary

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.

Details

Filter implementation: thumbor/filters/proportion.py
value is parsed as a float (BaseFilter.DecimalNumber) with no maximum.
The filter computes new_width = source_width * value and new_height = source_height * value and then calls engine.resize(new_width, new_height).
Execution phase: proportion runs in the default POST_TRANSFORM phase (after the main transform pipeline). This means it can effectively bypass request-level size clamping that happens earlier in the request lifecycle (e.g., MAX_WIDTH/MAX_HEIGHT applied to req.width/req.height).

Documentation states the percentage argument should be 0.0 to 1.0 (docs/proportion.rst), but the implementation does not enforce this constraint.

PoC

Preconditions

The proportion filter is enabled (it is enabled by default via BUILTIN_FILTERS).
Either:
/unsafe/ URLs are allowed (ALLOW_UNSAFE_URL=True, common default in some deployments), OR
/unsafe/ is disabled, and the attacker has a valid signed URL (i.e., the attacker is an authorized user/partner, or otherwise can obtain signed URLs issued by a trusted signing service).

Example request 1 (signed URL)

The following request was used to reproduce the issue and causes severe resource exhaustion:

http://<host>:<port>/<url-sign>/100x100/filters:proportion(10000)/example.jpg

Example request 2 (/unsafe/)

If /unsafe/ is enabled:

http://<host>:<port>/unsafe/100x100/filters:proportion(10000)/example.jpg

Impact

Remote Denial of Service via CPU and/or memory exhaustion (and potentially process crash / OOM kill).
Exploitability depends on deployment:
If /unsafe/ is enabled: unauthenticated remote DoS.
If /unsafe/ is disabled: the attacker needs a valid signed URL (i.e., the attacker can legitimately request signed URLs, or has access to signed URLs issued for other users/partners). If signed URLs are not exposed to untrusted parties, exploitability is reduced but the risk still applies to any party who can generate/use signed URLs.

Suggested remediation

Enforce a strict bound on the proportion parameter (e.g., 0.0 < value <= 1.0 as documented), or define a safe maximum based on intended semantics.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 7.7.7"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "thumbor"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.8.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53505"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-31T19:00:44Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nThumbor\u0027s `filters:proportion(\u003cvalue\u003e)` filter does not enforce an upper bound on `\u003cvalue\u003e` and runs in the post-transform phase. An attacker can trigger extremely large resizes (CPU/memory exhaustion) and cause denial of service.\n\n### Details\n- Filter implementation: `thumbor/filters/proportion.py`\n  - `value` is parsed as a float (`BaseFilter.DecimalNumber`) with no maximum.\n  - The filter computes `new_width = source_width * value` and `new_height = source_height * value` and then calls `engine.resize(new_width, new_height)`.\n- Execution phase: `proportion` runs in the default POST_TRANSFORM phase (after the main transform pipeline). This means it can effectively bypass request-level size clamping that happens earlier in the request lifecycle (e.g., `MAX_WIDTH`/`MAX_HEIGHT` applied to `req.width/req.height`).\n\nDocumentation states the `percentage` argument should be `0.0 to 1.0` (`docs/proportion.rst`), but the implementation does not enforce this constraint.\n\n### PoC\n#### Preconditions\n- The `proportion` filter is enabled (it is enabled by default via `BUILTIN_FILTERS`).\n- Either:\n  - `/unsafe/` URLs are allowed (`ALLOW_UNSAFE_URL=True`, common default in some deployments), OR\n  - `/unsafe/` is disabled, and the attacker has a valid signed URL (i.e., the attacker is an authorized user/partner, or otherwise can obtain signed URLs issued by a trusted signing service).\n\n#### Example request 1 (signed URL)\nThe following request was used to reproduce the issue and causes severe resource exhaustion:\n\n`http://\u003chost\u003e:\u003cport\u003e/\u003curl-sign\u003e/100x100/filters:proportion(10000)/example.jpg`\n\n#### Example request 2 (/unsafe/)\nIf `/unsafe/` is enabled:\n\n`http://\u003chost\u003e:\u003cport\u003e/unsafe/100x100/filters:proportion(10000)/example.jpg`\n\n### Impact\n- Remote Denial of Service via CPU and/or memory exhaustion (and potentially process crash / OOM kill).\n- Exploitability depends on deployment:\n  - If `/unsafe/` is enabled: unauthenticated remote DoS.\n  - If `/unsafe/` is disabled: the attacker needs a valid signed URL (i.e., the attacker can legitimately request signed URLs, or has access to signed URLs issued for other users/partners). If signed URLs are not exposed to untrusted parties, exploitability is reduced but the risk still applies to any party who can generate/use signed URLs.\n\n### Suggested remediation\n- Enforce a strict bound on the `proportion` parameter (e.g., `0.0 \u003c value \u003c= 1.0` as documented), or define a safe maximum based on intended semantics.",
  "id": "GHSA-phj3-59pf-cp83",
  "modified": "2026-07-31T19:00:44Z",
  "published": "2026-07-31T19:00:44Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/security/advisories/GHSA-phj3-59pf-cp83"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/commit/2c716119de986cfc68c7071af52a98187e006023"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/thumbor/thumbor"
    },
    {
      "type": "WEB",
      "url": "https://github.com/thumbor/thumbor/releases/tag/7.8.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

CVE-2026-53505 (GCVE-0-2026-53505)

GHSA-PHJ3-59PF-CP83

Summary

Details

PoC

Preconditions

Example request 1 (signed URL)

Example request 2 (/unsafe/)

Impact

Suggested remediation

Tags

Sightings

Nomenclature