CVE-2025-61771 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's 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 CVE-2025-61771.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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 |
Affected Products
rackrackDetection & 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 CVE-2025-61771 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
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 CVE-2025-61771 in your dependencies?
Find it across RubyGems, including transitive dependencies.