GHSA-w9pc-fmgc-vxvw is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in rack. A fix is available for rack — see the affected versions and patch details below.
Rack: Multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-w9pc-fmgc-vxvw.
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-w9pc-fmgc-vxvw 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 377,238 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
rack💎rack💎rackReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Rack::Multipart::Parser stores non-file form fields (parts without a filename) entirely in memory as Ruby String objects. A single large text field in a multipart/form-data request (hundreds of megabytes or more) can consume equivalent process memory, potentially leading to out-of-memory (OOM) conditions and denial of service (DoS).
Details
During multipart parsing, file parts are streamed to temporary files, but non-file parts are buffered into memory:
body = String.new # non-file → in-RAM buffer
@mime_parts[mime_index].body << content
There is no size limit on these in-memory buffers. As a result, any large text field—while technically valid—will be loaded fully into process memory before being added to params.
Impact
Attackers can send large non-file fields to trigger excessive memory usage. Impact scales with request size and concurrency, potentially leading to worker crashes or severe garbage-collection overhead. All Rack applications processing multipart form submissions are affected.
Mitigation
- Upgrade: Use a patched version of Rack that enforces a reasonable size cap for non-file fields (e.g., 2 MiB).
- Workarounds:
- Restrict maximum request body size at the web-server or proxy layer (e.g., Nginx
client_max_body_size). - Validate and reject unusually large form fields at the application level.
- Restrict maximum request body size at the web-server or proxy layer (e.g., Nginx
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack | all versions | 2.2.19bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.1&&< 3.1.17 | 3.1.17bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.2&&< 3.2.2 | 3.2.2bundle update rack --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rack to 2.2.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w9pc-fmgc-vxvw 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-w9pc-fmgc-vxvw can be triaged on real exposure rather than presence alone.
Tailored to GHSA-w9pc-fmgc-vxvw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
The impact is IMPORTANT because this happens over a network and causes a denial of service. Large non-file fields are buffered in memory instead of being streamed or capped, leading to memory exhaustion and worker crashes.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | pcs-0:0.12.0-3.el10_0.3 | RHSA-2025:19513 |
| Red Hat Enterprise Linux 10 | pcs-0:0.12.1-1.el10_1.1 | RHSA-2025:21036 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | pcs-0:0.9.169-3.el7_9.5 | RHSA-2025:21696 |
| Red Hat Enterprise Linux 8 | pcs-0:0.10.18-2.el8_10.7 | RHSA-2025:19719 |
| Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support | pcs-0:0.10.8-1.el8_4.8 | RHSA-2025:19948 |
| Red Hat Enterprise Linux 8.6 Telecommunications Update Service | pcs-0:0.10.12-6.el8_6.10 | RHSA-2025:19734 |
| Red Hat Enterprise Linux 8.8 Telecommunications Update Service | pcs-0:0.10.15-4.el8_8.9 | RHSA-2025:19647 |
| Red Hat Enterprise Linux 9 | pcs-0:0.11.9-2.el9_6.2 | RHSA-2025:19512 |
Frequently Asked Questions
Is GHSA-w9pc-fmgc-vxvw in your dependencies?
O3 Security finds GHSA-w9pc-fmgc-vxvw across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.