GHSA-phj3-59pf-cp83 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in thumbor. O3 Security confirms whether GHSA-phj3-59pf-cp83 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-phj3-59pf-cp83.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-phj3-59pf-cp83 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 374,847 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
thumborReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Thumbor's filters:proportion(<value>) filter does not enforce an upper bound on <value> 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.pyvalueis parsed as a float (BaseFilter.DecimalNumber) with no maximum.- The filter computes
new_width = source_width * valueandnew_height = source_height * valueand then callsengine.resize(new_width, new_height).
- Execution phase:
proportionruns 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_HEIGHTapplied toreq.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
proportionfilter is enabled (it is enabled by default viaBUILTIN_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 resource exhaustion:
http://<host>:<port>/<url-sign>/100x100/filters:proportion(10000)/example.jpg
Example request 2 (/unsafe/)
If /unsafe/ is enabled:
http://<host>:<port>/unsafe/100x100/filters:proportion(10000)/example.jpg
Impact
- Remote Denial of Service via CPU and/or memory exhaustion (and potentially process crash / OOM kill).
- Exploitability depends on deployment:
- If
/unsafe/is enabled: unauthenticated remote DoS. - If
/unsafe/is disabled: the attacker needs a valid signed URL (i.e., the attacker can legitimately request signed URLs, or has access to signed URLs issued for other users/partners). If signed URLs are not exposed to untrusted parties, exploitability is reduced but the risk still applies to any party who can generate/use signed URLs.
- If
Suggested remediation
- Enforce a strict bound on the
proportionparameter (e.g.,0.0 < value <= 1.0as documented), or define a safe maximum based on intended semantics.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | thumbor | all versions | 7.8.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for thumbor. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update thumbor to 7.8.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-phj3-59pf-cp83 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-phj3-59pf-cp83 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-phj3-59pf-cp83. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-phj3-59pf-cp83 in your dependencies?
O3 detects GHSA-phj3-59pf-cp83 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.