CVE-2026-39865 is a medium-severity (CVSS 5.9) Uncontrolled Resource Consumption vulnerability in axios. A fix is available for axios — see the affected versions and patch details below.
Axios HTTP/2 Session Cleanup State Corruption Vulnerability
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39865.
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-2026-39865 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
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.
axiosnpmDescription
Summary
Axios HTTP/2 session cleanup logic contains a state corruption bug that allows a malicious server to crash the client process through concurrent session closures. This denial-of-service vulnerability affects axios versions prior to 1.13.2 when HTTP/2 is enabled.
Details
The vulnerability exists in the Http2Sessions.getSession() method in lib/adapters/http.js. The session cleanup logic contains a control flow error when removing sessions from the sessions array.
Vulnerable Code:
while (i--) {
if (entries[i][0] === session) {
entries.splice(i, 1);
if (len === 1) {
delete this.sessions[authority];
return;
}
}
}
Root Cause:
After calling entries.splice(i, 1) to remove a session, the original code only returned early if len === 1. For arrays with multiple entries, the iteration continued after modifying the array, causing undefined behavior and potential crashes when accessing shifted array indices.
Fixed Code:
while (i--) {
if (entries[i][0] === session) {
if (len === 1) {
delete this.sessions[authority];
} else {
entries.splice(i, 1);
}
return;
}
}
The fix restructures the control flow to immediately return after removing a session, regardless of whether the array is being emptied or just having one element removed. This prevents continued iteration over a modified array and eliminates the state corruption vulnerability.
Affected Component:
lib/adapters/http.js- Http2Sessions class, session cleanup in connection close handler
PoC
- Set up a malicious HTTP/2 server that accepts multiple concurrent connections from an axios client
- Establish multiple concurrent HTTP/2 sessions with the axios client
- Close all sessions simultaneously with precise timing
- The flawed cleanup logic attempts to iterate over and modify the sessions array concurrently
- This causes the client to access invalid memory locations, resulting in a process crash
Prerequisites:
- Client must use axios with HTTP/2 enabled
- Client must connect to attacker-controlled HTTP/2 server
- Multiple concurrent HTTP/2 sessions must be established
- Server must close all sessions simultaneously with precise timing
Impact
Who is impacted:
- Applications using axios with HTTP/2 enabled
- Applications connecting to untrusted or attacker-controlled HTTP/2 servers
- Node.js applications using axios for HTTP/2 requests
Impact Details:
- Denial of Service: Malicious server can crash the axios client process by accepting and closing multiple concurrent HTTP/2 connections simultaneously
- Availability Impact: Complete loss of availability for the client process through crash (though service may auto-restart)
- Scope: Impact is limited to the single client process making the requests; does not escape to affect other components or systems
- No Confidentiality or Integrity Impact: Vulnerability only causes process crash, no information disclosure or data modification
CVSS Score: 5.9 (Medium) CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE Classifications:
- CWE-400: Uncontrolled Resource Consumption
- CWE-662: Improper Synchronization
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | axios | ≥ 1.13.0&&< 1.13.2 | 1.13.2npm install axios@1.13.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for axios, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update axios to 1.13.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39865 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-2026-39865 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-39865. 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-2026-39865 in your dependencies?
O3 Security finds CVE-2026-39865 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.