Cross-Site Scripting (XSS) in telejson (CVE-2026-47099)
Summary
Cross-site scripting in telejson (CVE-2026-47099). Risk of unauthorized operations or information disclosure. Exploitable via postMessage. Mitigation: upgrade to 6.0.0 or later.
Original description
The description as published by the source.
Summary
telejson versions prior to 6.0.0 (released 2022) are vulnerable to DOM-based Cross-Site Scripting (XSS) through unsafe deserialisation. Attacker-controlled input from the _constructor-name_ property in parsed JSON is passed directly to new Function() without sanitisation, allowing arbitrary JavaScript execution.
Affected versions
| Package | Affected | Fixed |
|---|---|---|
| telejson | < 6.0.0 | >= 6.0.0 |
Details
telejson's parse() function uses a custom reviver to reconstruct JavaScript objects from serialised JSON. When processing objects with a _constructor-name_ property, the reviver passes the constructor name directly to new Function() to recreate the object's prototype.
In versions prior to 6.0.0, this constructor name is not sanitised. An attacker who can deliver a crafted JSON payload to telejson.parse() (for example, via postMessage in applications that use telejson for cross-frame communication) can inject arbitrary JavaScript into the new Function() call.
Vulnerable code (src/index.ts, lines 293-299 at v5.3.3):
if (isObject(value) && value['_constructor-name_']) {
const name = value['_constructor-name_'];
if (name !== 'Object') {
const Fn = new Function(`return function ${name}(){}`)();
Object.setPrototypeOf(value, new Fn());
}
Fixed code ([src/index.ts, lines 340-346 a…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-47099 has been found in telejson.
Attackers can target a specific entry point like postMessage over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 6.1/10.
What to do: upgrade telejson to 6.0.0 or later.
If unsure, ask your IT team or search "telejson CVE-2026-47099" on the vendor's site.
CVE-2026-47099 (telejson) — CWE-79 / CVSS v3 6.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: postMessage / allowFunction
Patched: 6.0.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Cross-site scripting (XSS) (CWE-79) exists in telejson. Attackers reach the vulnerable code path via postMessage without authentication.
Check the vendor advisory for the affected versions of telejson. Attack surface: postMessage / allowFunction.
Severity: Medium (CVSS 6.1/10). Risk of unauthorized operations or information disclosure.
Update to 6.0.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'telejson' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'telejson' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
telejsonを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade telejson to 6.0.0ステージング環境で 6.0.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web disclosure@vulncheck.com
- web github.com
- web disclosure@vulncheck.com
- web disclosure@vulncheck.com