Vulnerability in thumbor (CVE-2026-53503)
Summary
Vulnerability in thumbor (CVE-2026-53503). Risk of unauthorized operations or information disclosure. Exploitable via columns_count. Mitigation: upgrade to 7.8.0 or later.
Original description
The description as published by the source.
Summary
Thumbor's filters:convolution(, , ) filter passes the user-controlled `` value to a C extension (thumbor/ext/filters/_convolution.c) where it is used as a divisor (for % and /) without validating columns > 0. When columns=0, the C code triggers undefined behavior; on x86_64 this reliably results in a fatal divide-by-zero trap (SIGFPE) and crashes the Thumbor process (confirmed on Linux x86_64 and macOS Intel x86_64), causing a remote denial of service.
Details
Root cause
The Python filter accepts columns=0, and the native C extension uses columns_count as a divisor without validating it.
- Python filter entry point allows
columns=0(thumbor/filters/convolution.py):
@filter_method(
r"(?:[-]?[\d]+\.?[\d]*[;])*(?:[-]?[\d]+\.?[\d]*)",
BaseFilter.PositiveNumber, # accepts 0
BaseFilter.Boolean,
)
async def convolution(self, matrix, columns, should_normalize=True):
...
imgdata = _convolution.apply(..., matrix, columns, should_normalize)
BaseFilter.PositiveNumber matches "0" (thumbor/filters/__init__.py):
class BaseFilter:
PositiveNumber = {"regex": r"[\d]+", "parse": int} # matches "0"
PositiveNonZeroNumber = {"regex": r"[\d]*[1-9][\d]*", "parse": int}
- C extension divides/modulos by
columns_countwithout a zero check (thumbor/ext/filters/_convolution.c):
kernel_size = PyTuple_Size(kernel_tuple);
if ((kernel_size % columns_count != 0) ||
(kernel_size % 2 == 0)…
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-2026-53503 has been found in thumbor.
Attackers can target a specific entry point like columns_count 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-2026-53503" on the vendor's site.
CVE-2026-53503 (thumbor) — CWE-20 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: columns_count / BaseFilter.PositiveNumber / convolution / BUILTIN_FILTERS
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-20) exists in thumbor. Attackers reach the vulnerable code path via columns_count without authentication.
Check the vendor advisory for the affected versions of thumbor. Attack surface: columns_count / BaseFilter.PositiveNumber / convolution / BUILTIN_FILTERS.
Severity: High (CVSS 7.5/10). 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
- Ubuntu UBUNTU-CVE-2026-53503 thumbor
References
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com