How severe is GHSA-p543-xpfm-54cp?

GHSA-p543-xpfm-54cp has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-p543-xpfm-54cp?

GHSA-p543-xpfm-54cp affects the following packages: rack (RubyGems), rack (RubyGems), rack (RubyGems). Ecosystems affected: RubyGems.

How do I fix GHSA-p543-xpfm-54cp?

Update rack to 2.2.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-p543-xpfm-54cp is resolved across your whole dependency graph.

How do I detect GHSA-p543-xpfm-54cp in my RubyGems dependencies?

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.

How do I mitigate GHSA-p543-xpfm-54cp if there is no patch (or I can't update yet)?

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 does O3 Security protect against GHSA-p543-xpfm-54cp?

O3 pinpoints whether GHSA-p543-xpfm-54cp is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is GHSA-p543-xpfm-54cp actively exploited in the wild?

No public exploit code has been indexed for GHSA-p543-xpfm-54cp yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-p543-xpfm-54cp?

GHSA-p543-xpfm-54cp has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 53th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-p543-xpfm-54cp?

GHSA-p543-xpfm-54cp is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-p543-xpfm-54cp published, and has it been updated?

GHSA-p543-xpfm-54cp was published on October 7, 2025 and was last updated on February 4, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎 RubyGems

GHSA-p543-xpfm-54cp

HIGH

Rack's unbounded multipart preamble buffering enables DoS (memory exhaustion)

Also known asCVE-2025-61770

Published

Oct 7, 2025

Updated

Feb 4, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk53th percentile+0.58%

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.

Blast Radius

3 pkgs affected

💎rack💎rack💎rack

Real-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 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.

Details

While searching for the first boundary, the parser appends incoming data into a shared buffer (@sbuf.concat(content)) and scans for the boundary pattern:

@sbuf.scan_until(@body_regex)

If the boundary is not yet found, the parser continues buffering data indefinitely. There is no trimming or size cap on the preamble, allowing attackers to send arbitrary amounts of data before the first boundary.

Impact

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.

Mitigation

Upgrade: Use a patched version of Rack that enforces a preamble size limit (e.g., 16 KiB) or discards preamble data entirely per RFC 2046 § 5.1.1.
Workarounds:
- Limit total request body size at the proxy or web server level.
- Monitor memory and set per-process limits to prevent OOM conditions.

Affected Packages

3 total 3 fixed

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 dependency

Detect
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 GHSA-p543-xpfm-54cp 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-p543-xpfm-54cp 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-p543-xpfm-54cp. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## Summary `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. ## Details While searching for the first boundary, the parser appends incoming data into a shared buffer (`@sbuf.concat(content)`) and scans for the boundary pattern: ```ruby @sbuf.scan_until(@body_regex) ``` If the boundary is not yet found, the parser continues buffering data

O3 Security · Impact-Aware SCA

Is GHSA-p543-xpfm-54cp in your dependencies?

O3 detects GHSA-p543-xpfm-54cp across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works