How severe is CVE-2025-25200?

No CVSS score has been assigned to CVE-2025-25200 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-25200?

CVE-2025-25200 affects the following packages: koa (npm), koa (npm), koa (npm), koa (npm). Ecosystems affected: npm.

How do I fix CVE-2025-25200?

Update koa to 2.15.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-25200 is resolved across your whole dependency graph.

How do I detect CVE-2025-25200 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for koa, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2025-25200 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.

Is CVE-2025-25200 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-25200 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 CVE-2025-25200?

CVE-2025-25200 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 58th 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 CVE-2025-25200?

CVE-2025-25200 is classified as CWE-1333 (CWE-1333). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-25200 published, and has it been updated?

CVE-2025-25200 was published on February 12, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2025-25200 — koa

Fix: koajs/koa@5054af6

CVE-2025-25200 is a CWE-1333 vulnerability in koa. A fix is available for koa — see the affected versions and patch details below.

Koa has Inefficient Regular Expression Complexity

Also known asGHSA-593f-38f6-jp5m

Published

Feb 12, 2025

Updated

Oct 28, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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-2025-25200.

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs58th percentile — riskier than 58% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

4 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

8Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

koanpm

9.8Mdownloads / week

Description

Koa is expressive middleware for Node.js using ES2017 async functions. Prior to versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3, Koa uses an evil regex to parse the X-Forwarded-Proto and X-Forwarded-Host HTTP headers. This can be exploited to carry out a Denial-of-Service attack. Versions 0.21.2, 1.7.1, 2.15.4, and 3.0.0-alpha.3 fix the issue.

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`koa`	≥ 2.0.0&&< 2.15.4	2.15.4`npm install koa@2.15.4`
📦npm	`koa`	≥ 3.0.0-alpha.0&&< 3.0.0-alpha.3	3.0.0-alpha.3`npm install koa@3.0.0-alpha.3`
📦npm	`koa`	≥ 1.0.0&&< 1.7.1	1.7.1`npm install koa@1.7.1`
📦npm	`koa`	all versions	0.21.2`npm install koa@0.21.2`

Affected Products

1 product · 6 configurations

Application

koakoajs

≥ 2.0.0 && < 2.15.4

1 version

3.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for koa, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update koa to 2.15.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-25200 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.

Frequently Asked Questions

### Summary Koa uses an evil regex to parse the `X-Forwarded-Proto` and `X-Forwarded-Host` HTTP headers. This can be exploited to carry out a Denial-of-Service attack. ### PoC Coming soon. ### Impact This is a Regex Denial-of-Service attack and causes memory exhaustion. The regex should be improved and empty values should not be allowed.

O3 Security · Impact-Aware SCA

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