Executive Summary
CVE-2026-13311 is a high-severity Denial of Service (DoS) vulnerability affecting the widely used Node.js package shell-quote (versions up to and including 1.8.4). The vulnerability stems from quadratic algorithmic complexity in the parse() function, which can be exploited remotely by unauthenticated attackers to block the Node.js event loop, resulting in service outages and degraded availability. This advisory provides a comprehensive technical analysis, exploitation context, affected versions, mitigation guidance, and references for further action.
Technical Information
CVE-2026-13311 is classified as a Denial of Service vulnerability due to inefficient algorithmic complexity (CWE-407) in the parse() function of the shell-quote npm package. The vulnerability is present in all versions up to and including 1.8.4. The root cause is the use of Array.prototype.concat within a reduce operation to finalize the token list. Each invocation of prev.concat(arg) copies the entire growing array, resulting in O(n²) time complexity relative to the number of input tokens. This allows an attacker to supply a crafted string—such as a long sequence of space-separated words—to any code path that calls parse(), blocking the single-threaded Node.js event loop for extended periods.
No shell metacharacters are required for exploitation; input filters for characters such as ;, |, $, or backticks do not mitigate this issue. The vulnerability is strictly related to algorithmic complexity and does not enable code execution or data disclosure.
Proof of Concept (PoC):
const { parse } = require('shell-quote');
const ms = fn => { const t = process.hrtime.bigint(); fn(); return Number(process.hrtime.bigint() - t) / 1e6; };
for (const N of [16000, 32000, 64000, 128000]) {
console.log(N, 'tokens ->', ms(() => parse('x '.repeat(N))).toFixed(0), 'ms');
}
Observed Results (on shell-quote@1.8.4, Node v24):
Input (tokens) | Bytes | parse() Time | Ratio vs prev (2× input)
|
16,000 | 32KB | 678 ms | — |
32,000 | 64KB | 4,169 ms | ×6.2 |
64,000 | 128KB | 14,914 ms | ×3.6 |
128,000 | 256KB | 57,319 ms | ×3.8 |
A ~128KB input blocks the event loop for approximately 15 seconds; ~256KB for nearly a minute. Larger payloads can block the event loop for several minutes, causing a complete denial of service for all concurrent clients.
CVSS v3.1 Base Score: 7.5 (High) CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0 Base Score: 8.7 (High) CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness: CWE-407 (Inefficient Algorithmic Complexity)
Threat Actor Profile
There is currently no evidence of widespread exploitation of CVE-2026-13311 in the wild. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog as of June 2026, and there are no public reports of active exploitation campaigns. However, the public availability of proof-of-concept code and the ease of exploitation make it likely that opportunistic attackers could leverage this vulnerability for denial-of-service attacks, especially against exposed Node.js services that utilize shell-quote for user input parsing.
A minimal HTTP server calling parse() on the request body, when hit with a single POST of 'x '.repeat(32000) (~63KB), froze for approximately 4.5 seconds. Concurrent GET requests were stalled for up to 4.3 seconds during this period, demonstrating the real-world impact of the vulnerability.
Technical Analysis of Malware/TTPs
As of the time of writing, there is no public evidence or attribution linking any Advanced Persistent Threat (APT) groups or organized threat actors to the exploitation of CVE-2026-13311. The vulnerability is generic and can be exploited by any remote, unauthenticated attacker. While no targeted campaigns have been observed, the simplicity of the attack vector and the public availability of exploit code increase the risk of adoption in opportunistic denial-of-service campaigns.
Exploitation in the Wild
The affected product is the shell-quote npm package, maintained by ljharb. All versions from 0.0.0 up to and including 1.8.4 are vulnerable. The issue is resolved in versions 1.8.5 and later, including 1.9.0.
Affected versions: 0.0.0 through 1.8.4 Patched versions: 1.8.5, 1.9.0 and later
Victimology and Targeting
The vulnerability is generic and not known to be targeted at any specific sector, country, or organization type. Any Node.js service using a vulnerable version of shell-quote and parsing user input is at risk.
Mitigation and Countermeasures
The primary mitigation is to upgrade shell-quote to version 1.8.5 or later (preferably 1.9.0). Organizations unable to upgrade immediately should implement input length caps on any user input passed to parse() as a temporary measure. Monitoring for abnormal request patterns, such as repeated requests with large, space-separated strings, is also recommended. Input validation and rate limiting can further reduce the risk of exploitation.
References
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