CVE-2025-8101 - Linkify Allows Prototype Pollution & HTML Attribute Injection (XSS)

CVE-2025-8101 + Linkify Allows Prototype Pollution & HTML Attribute Injection (XSS) + High + 2025-07-26

One-sentence business risk

Server-side request forgery can bridge from the public app into cloud metadata and private network services.

Research notes

  • Root cause: Prototype Pollution in internal assign() helper in Linkify allows remote attackers to execute arbitrary JavaScript (Stored or Reflected XSS) via injection of event handlers through unfiltered proto property.
  • Affected versions: npm:linkifyjs = 4.3.1.
  • Fixed / safe versions: 4.3.2.
  • Public exploit / PoC signal: the consulted NVD/GHSA/vendor sources describe the trigger class; treat it as reproducible until patched.
  • CVSS: use upstream advisory score .

Exact vulnerable code pattern

setPath(target, key.split("."), value)  # no segment denylist

Fixed / mitigated code pattern

reject segments in {"__proto__", "constructor", "prototype"} before walking the object

Dependency or runtime update:

npm ls linkifyjs || true
npm install linkifyjs@latest --save-exact
npm audit --omit=dev

Step-by-step integration guide

  1. Inventory linkifyjs across source, lockfiles, SBOMs, container images, CI images, and deployment manifests.
  2. Upgrade to 4.3.2 or apply the exact vendor patch referenced below.
  3. Replace the vulnerable prototype-pollution pattern with the fixed pattern and fail closed on malformed input.
  4. Add a regression test that exercises the advisory trigger and proves the request is rejected, bounded, or authorized.
  5. Deploy through canary, monitor security logs and resource metrics, then remove temporary edge blocks only after all runtimes are fixed.

Alternative mitigations

  • Disable the vulnerable feature path while the package/runtime update rolls out.
  • Add WAF or reverse-proxy rules for traversal tokens, prototype-polluting keys, oversized frames, shell metacharacters, or unauthenticated tool calls matching the trigger class.
  • Restrict internal egress, rotate exposed secrets, and revoke affected tokens/keys if the vulnerability can disclose config, logs, JWT secrets, proxy credentials, or PKI material.
  • For admin/API authorization issues, temporarily require elevated roles and explicit ownership checks at the gateway.

Detection signature

id: cve-2025-8101-linkify-allows-prototype-pollution-html-attribut
source: GitHub Advisory Database
dependency_or_product: "linkifyjs"
affected: "npm:linkifyjs = 4.3.1"
fixed: "4.3.2"
signals:
  - "prototype-pollution"
  - "../"
  - "__proto__"
  - "tools/call"
  - "wp_ajax_nopriv"
  - "pickle.loads"
  - "shell command construction"
action: "upgrade, add regression test, and verify deploy artifact"

Copy-paste skill

You are remediating CVE-2025-8101 (Linkify Allows Prototype Pollution & HTML Attribute Injection (XSS)) in this repository.

Find every affected dependency, runtime, image, service configuration, and reachable code path. Upgrade or patch to 4.3.2. Replace the vulnerable prototype-pollution pattern with a fail-closed implementation, add a regression test for the trigger shape, and update deployment/SBOM artifacts. If this repository does not control the affected runtime, create TRIAGE.md naming the owner, affected version, fixed version, and blocking decision.

Keywords, affected tech stack, and revenue tags

  • Keywords: CVE-2025-8101, prototype-pollution, linkifyjs, GitHub Advisory Database.
  • Affected tech stack: javascript/npm.
  • Revenue tags: sellable_to_fintech, enterprise_blocker, high_priority_sla.

References