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CVE-2026-53500 high CVSS 8.2

Vulnerability in thumbor (CVE-2026-53500)

Summary

Vulnerability in thumbor (CVE-2026-53500). Confidential information can be exposed externally. Exploitable via ALLOWED_SOURCES. Mitigation: upgrade to 7.8.0 or later.

Original description

The description as published by the source.

Summary

The ALLOWED_SOURCES configuration is meant to restrict which hosts Thumbor's HTTP loader may fetch images from. Plain-string entries in that list (the overwhelming majority of real-world and documented configurations) are passed directly to re.match() without escaping. Because . is a regex wildcard, every dot in a domain name becomes a bypass vector: s.glbimg.com silently matches sXglbimgYcom, sAglbimg.com, and any other hostname that differs only at a dot position. This undermines the primary SSRF defence that ALLOWED_SOURCES is intended to provide.

Affected component

thumbor/loaders/http_loader.py — validate()

Proof of concept

import re
from thumbor.config import Config
from thumbor.context import Context
from thumbor.loaders import http_loader as loader

config = Config()
config.ALLOWED_SOURCES = ["s.glbimg.com"]   # typical user config
ctx = Context(None, config, None)

# These should be blocked — both return True due to the unescaped dot
print(loader.validate(ctx, "http://sXglbimgYcom/secret.jpg"))  # True ← bypass
print(loader.validate(ctx, "http://sAglbimg.com/secret.jpg"))  # True ← bypass

# Legitimate origin — correctly allowed
print(loader.validate(ctx, "http://s.glbimg.com/logo.jpg"))    # True ← correct

Root cause

thumbor/loaders/http_loader.py (before fix):

for pattern in context.config.ALLOWED_SOURCES:
    if isinstance(pattern, Pattern):
        match = url
    else:
        pattern = f"^{…

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-2026-53500 has been found in thumbor.
Attackers can target a specific entry point like ALLOWED_SOURCES over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.2/10.
What to do: upgrade thumbor to 7.8.0 or later.
If unsure, ask your IT team or search "thumbor CVE-2026-53500" on the vendor's site.

CVE-2026-53500 (thumbor) — CWE-1333 / CVSS v3 8.2
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: ALLOWED_SOURCES / s.glbimg.com / sXglbimgYcom / sAglbimg.com
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-1333) exists in thumbor. Attackers reach the vulnerable code path via ALLOWED_SOURCES without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of thumbor. Attack surface: ALLOWED_SOURCES / s.glbimg.com / sXglbimgYcom / sAglbimg.com.

🔥 Severity

Severity: High (CVSS 8.2/10). Confidential information can be exposed externally.

🔧 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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