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CVE-2026-53505 high CVSS 7.5

Vulnerability in thumbor (CVE-2026-53505)

Summary

Vulnerability in thumbor (CVE-2026-53505). Risk of unauthorized operations or information disclosure. Exploitable via value. Mitigation: upgrade to 7.8.0 or later.

Original description

The description as published by the source.

Summary

Thumbor's filters:proportion() filter does not enforce an upper bound on `` 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…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-53505 has been found in thumbor.
Attackers can target a specific entry point like value over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade thumbor to 7.8.0 or later.
If unsure, ask your IT team or search "thumbor CVE-2026-53505" on the vendor's site.

CVE-2026-53505 (thumbor) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: value / BaseFilter.DecimalNumber / proportion / MAX_WIDTH
Patched: 7.8.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-400) exists in thumbor. Attackers reach the vulnerable code path via value without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of thumbor. Attack surface: value / BaseFilter.DecimalNumber / proportion / MAX_WIDTH.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 7.8.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'thumbor' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'thumbor' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で thumbor を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade thumbor to 7.8.0

    ステージング環境で 7.8.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip thumbor
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.8.0"}]}]
PyPI thumbor
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.8.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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