Vulnerability in thumbor (CVE-2026-53501)
Summary
Vulnerability in thumbor (CVE-2026-53501). Data can be tampered with by attackers. Exploitable via url_to_validate. Mitigation: upgrade to 7.8.0 or later.
Original description
The description as published by the source.
HMAC validation bypass via multiple .replace() calls when removing URL signature
Summary
Thumbor’s HMAC validation can be bypassed due to the use of Python’s .replace() when removing the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation.
This allows crafting URLs where the validated string differs from the actual requested resource, enabling loading images from unintended domains or paths.
Details
Thumbor signs URLs using HMAC-SHA1 to prevent abuse such as loading arbitrary external images or invoking filters without authorization.
During request validation, Thumbor removes the signature from the request URL before recalculating the HMAC. The relevant code:
url_signature = self.context.request.hash
if url_signature:
signer = self.context.modules.url_signer(
self.context.server.security_key
)
try:
quoted_hash = quote(self.context.request.hash)
except KeyError:
self._error(400, f"Invalid hash: {self.context.request.hash}")
return
url_to_validate = url.replace(
f"/{self.context.request.hash}/", ""
).replace(f"/{quoted_hash}/", "")
valid = signer.validate(
unquote(url_signature).encode(), url_to_validate
)
The issue is that .replace() removes every occurrence of the substring in the U…
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-2026-53501 has been found in thumbor.
Attackers can target a specific entry point like url_to_validate over the network to misuse the product.
Data can be tampered with by attackers. 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-2026-53501" on the vendor's site.
CVE-2026-53501 (thumbor) — CWE-347 / CVSS v3 8.2
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: url_to_validate
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.
A vulnerability (CWE-347) exists in thumbor. Attackers reach the vulnerable code path via url_to_validate without authentication.
Check the vendor advisory for the affected versions of thumbor. Attack surface: url_to_validate.
Severity: High (CVSS 8.2/10). Data can be tampered with by attackers.
Update to 7.8.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
-
1Identify 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。 -
2Apply 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。
-
3Post-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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-53501 thumbor Fixed in: 7.8.0-1
- Ubuntu UBUNTU-CVE-2026-53501 thumbor
References
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com