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CVE-2026-55536 – Unauthenticated WebSocket Session Hijacking (Origin-Check Bypass) – PraisonAI Brows

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Summary

CVE-2026-55536 is a critical origin-validation bypass in PraisonAI’s Browser Server component, which is responsible for authorizing WebSocket connections from a companion Chrome extension. The server checks incoming connection origins against the pattern chrome-extension://[a-z0-9]{32} using Python’s re.match(), which only anchors the beginning of the string, allowing attacker-supplied origins with extra trailing characters to pass validation. Once bypassed, an unauthenticated remote attacker can issue start_session and other browser-automation commands over the WebSocket, resulting in cookie theft, screenshot capture, and unauthorized actions on a victim’s authenticated web sessions. The flaw carries a CVSS v3.1 base score of 9.1 (Critical) and requires no privileges or user interaction.

Technical details

  • Root cause: praisonai/browser/server.py validates the Origin header of incoming WebSocket connections using re.match("chrome-extension://[a-z0-9]{32}", origin). Because re.match() only anchors the start of the string (not the end), an origin such as chrome-extension:// followed by 32 valid characters plus arbitrary additional characters still satisfies the check.
  • Weakness classification: CWE-284 (Improper Access Control) and CWE-625 (Permissive Regular Expression).
  • Notably, this is a patch-bypass issue: it re-opens a variant of a previously patched WebSocket/browser-bridge authentication weakness (related advisory covering CVE-2026-40289) by working around the origin-check logic that was intended to close that gap.
  • Trigger conditions: The target must be running a vulnerable version of PraisonAI’s Browser Server with the WebSocket bridge exposed and reachable by the attacker over the network.
  • Attack vector: Network (AV:N), no authentication or privileges required (PR:N), no user interaction (UI:N), low attack complexity (AC:L).
  • Impact: High confidentiality and integrity impact (C:H/I:H) — an attacker can hijack the browser automation session to steal cookies/session tokens, capture screenshots of authenticated pages, and perform unauthorized actions on any site the victim’s browser is authenticated to. No direct availability impact (A:N).

Affected software

  • PraisonAI (pip package praisonai) versions up to and including 4.6.52 are vulnerable.
  • Fixed in praisonai 4.6.58 and later.

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Mitigation and recommended actions

  • Immediate: Upgrade PraisonAI to version 4.6.58 or later, which replaces the unanchored re.match() origin check with a properly bounded validation (e.g., re.fullmatch() restricted to valid Chrome extension ID characters).
  • If immediate patching is not possible:
    • Restrict network access to the PraisonAI Browser Server’s WebSocket endpoint to trusted hosts only (e.g., localhost-only binding or firewall/network segmentation).
    • Disable or avoid running the browser automation/bridge component on internet-exposed hosts until patched.
    • Monitor for unexpected WebSocket connections or start_session commands originating from unrecognized clients.
  • After upgrading, review browser automation session logs for signs of prior exploitation, and rotate any credentials/session cookies that may have been exposed through affected browser sessions.

References

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