CVE-2025-61919 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 is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
Exploitation Status
No confirmed exploitation observed yet
- 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 CVE-2025-61919.
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
CVE-2025-61919 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 377,636 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::Request#POST reads the entire request body into memory for Content-Type: application/x-www-form-urlencoded, calling rack.input.read(nil) without enforcing a length or cap. Large request bodies can therefore be buffered completely into process memory before parsing, leading to denial of service (DoS) through memory exhaustion.
Details
When handling non-multipart form submissions, Rack’s request parser performs:
form_vars = get_header(RACK_INPUT).read
Since read is called with no argument, the entire request body is loaded into a Ruby String. This occurs before query parameter parsing or enforcement of any params_limit. As a result, Rack applications without an upstream body-size limit can experience unbounded memory allocation proportional to request size.
Impact
Attackers can send large application/x-www-form-urlencoded bodies to consume process memory, causing slowdowns or termination by the operating system (OOM). The effect scales linearly with request size and concurrency. Even with parsing limits configured, the issue occurs before those limits are enforced.
Mitigation
- Update to a patched version of Rack that enforces form parameter limits using
query_parser.bytesize_limit, preventing unbounded reads ofapplication/x-www-form-urlencodedbodies. - Enforce strict maximum body size at the proxy or web server layer (e.g., Nginx
client_max_body_size, ApacheLimitRequestBody).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack | all versions | 2.2.20bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.0&&< 3.1.18 | 3.1.18bundle update rack --conservative |
| 💎RubyGems | rack | ≥ 3.2&&< 3.2.3 | 3.2.3bundle 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 2.2.20 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-61919 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 CVE-2025-61919 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-61919. 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.
~~~ Affectedness: Rack 1.x, including 1.6.x, is not affected by this vulnerability. The issue exists only in Rack 2.x and 3.x, where request parsing was refactored into the QueryParser component. Since Rack 1.x does not include this component, it does not contain the vulnerable logic. Ruby 2.x and 3.x versions shipped…
| 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 CVE-2025-61919 in your dependencies?
O3 Security finds CVE-2025-61919 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.