CVE-2025-61770
HIGHCVE-2025-61770 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in rack. O3 Security confirms whether CVE-2025-61770 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion)
Blast Radius
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
Rack is a modular Ruby web server interface. In versions prior to 2.2.19, 3.1.17, and 3.2.2, Rack::Multipart::Parser buffers the entire multipart preamble (bytes before the first boundary) in memory without any size limit. A client can send a large preamble followed by a valid boundary, causing significant memory use and potential process termination due to out-of-memory (OOM) conditions. Remote attackers can trigger large transient memory spikes by including a long preamble in multipart/form-data requests. The impact scales with allowed request sizes and concurrency, potentially causing worker crashes or severe slowdown due to garbage collection. Versions 2.2.19, 3.1.17, and 3.2.2 enforce a preamble size limit (e.g., 16 KiB) or discard preamble data entirely. Workarounds include limiting total request body size at the proxy or web server level and monitoring memory and set per-process limits to prevent OOM conditions.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | rack | all versions | 2.2.19 |
| 💎RubyGems | rack | ≥ 3.1&&< 3.1.17 | 3.1.17 |
| 💎RubyGems | rack | ≥ 3.2&&< 3.2.2 | 3.2.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rack. 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 rack to 2.2.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-61770 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 CVE-2025-61770 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 CVE-2025-61770. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-61770 in your dependencies?
O3 detects CVE-2025-61770 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.