Path Traversal in thumbor (CVE-2026-53502)
Summary
Path traversal in thumbor (CVE-2026-53502). Risk of unauthorized operations or information disclosure. Exploitable via imaging.py. Mitigation: upgrade to 7.8.0 or later.
Original description
The description as published by the source.
The file_loader performs unquote() on the file path AFTER the abspath() + startswith() security check. An attacker can use percent-encoded path traversal sequences (%2e%2e for ..) that pass the security check as literal directory names, but are then decoded to actual .. traversal sequences.
Affected code
thumbor/loaders/file_loader.py lines 28-49:
async def load(context, path):
file_path = join(
context.config.FILE_LOADER_ROOT_PATH.rstrip("/"), path.lstrip("/")
)
file_path = abspath(file_path)
inside_root_path = file_path.startswith( # Security check
abspath(context.config.FILE_LOADER_ROOT_PATH)
)
result = LoaderResult()
if not inside_root_path:
result.error = LoaderResult.ERROR_NOT_FOUND
result.successful = False
return result
if not exists(file_path):
file_path = unquote(file_path) # unquote AFTER check!
if exists(file_path) and isfile(file_path):
with open(file_path, "rb") as source_file:
...
The watermark and frame filters pass their URL parameters directly to the loader without re-encoding (unlike the main image URL flow which applies quote() in imaging.py line 37).
PoC
# Read /etc/passwd via watermark filter path traversal
# %252e is double-encoded: Tornado decodes to %2e, filter passes to file_loader,
# file_loader unquote decodes %2e to .
curl 'http://thumbor-host:8888/unsafe/filters:watermark(…
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-2026-53502 has been found in thumbor.
Attackers can target a specific entry point like imaging.py over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade thumbor to 7.8.0 or later.
If unsure, ask your IT team or search "thumbor CVE-2026-53502" on the vendor's site.
CVE-2026-53502 (thumbor) — CWE-22
Attack surface: imaging.py / file_loader_http_fallback
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.
Path traversal (CWE-22) exists in thumbor. Attackers reach the vulnerable code path via imaging.py.
Check the vendor advisory for the affected versions of thumbor. Attack surface: imaging.py / file_loader_http_fallback.
Severity: ?. Risk of unauthorized operations or information disclosure.
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-2026-53502 thumbor Fixed in: 7.8.0-1
- Ubuntu UBUNTU-CVE-2026-53502 thumbor
References
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com