CVE-2021-39176 is a high-severity (CVSS 7.5) CWE-401 vulnerability in detect-character-encoding. 1 public exploit reference exists, so weaponization risk is real. A fix is available for detect-character-encoding — see the affected versions and patch details below.
Missing Release of Memory after Effective Lifetime in detect-character-encoding
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-39176 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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.
detect-character-encodingnpmDescription
Impact
In detect-character-encoding v0.3.0 and earlier, allocated memory is not released.
Patches
The problem has been patched in detect-character-encoding v0.3.1.
CVSS score
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/RL:O/RC:C
Base Score: 7.5 (High) Temporal Score: 7.2 (High)
Since detect-character-encoding is a library, the scoring is based on the “reasonable worst-case implementation scenario”, namely, using detect-character-encoding in a program accessible over the internet which becomes unavailable when running out of memory. Depending on your specific implementation, the vulnerability’s severity in your program may be different.
Proof of concept
const express = require("express");
const detectCharacterEncoding = require("detect-character-encoding");
const app = express();
app.get("/", (req, res) => {
detectCharacterEncoding(Buffer.from("foo"));
res.end();
});
app.listen(3000);
hey -n 1000000 http://localhost:3000 (hey) causes the Node.js process to consume more and more memory.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | detect-character-encoding | all versions | 0.3.1npm install detect-character-encoding@0.3.1 |
Affected Products
detect-character-encodingdetect-character-encoding_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for detect-character-encoding, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update detect-character-encoding to 0.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39176 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
Is CVE-2021-39176 in your dependencies?
Find it across npm, including transitive dependencies.