External risk intelligence

Bookcars JWT Authentication Bypass Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-36721

A vulnerability in bookcars' `validateAccessToken` function allows attackers to bypass authentication by submitting a forged JWT token. This could lead to unauthorized access to application functions and potentially sensitive information. Determining if bookcars is used within the environment is the primary concern.

4Halo Surface Signal

External exposure likelihood

Halo Surface Signal score for CVE-2026-36721

The vulnerability exists in the authentication validation process of a web-based application (bookcars). Web applications handling authentication tokens are commonly deployed as internet-facing services to allow remote user access, making this a likely target for external network exposure.

PCI scan relevance

PCI Relevance for CVE-2026-36721

Yes

CVE-2026-36721 — Halo PCI Relevance: Yes. Under typical PCI ASV external scan criteria, this issue may be flagged for scan prioritization.

This vulnerability allows attackers to bypass authentication via a forged JWT token, which could lead to an ASV scan failure due to authentication bypass.

Scan-prioritization guidance only—not a PCI DSS certification or ASV attestation.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in the bookcars system that could allow unauthorized access by bypassing authentication. This issue lies within the system's handling of access tokens. The primary concern at this stage is to determine if this specific technology is in use within our environment and, if so, to what extent.

  • Access tokens can be forged.
  • Important for confirming potential access bypass.
  • Verify if bookcars is in use.

Attack Path

How an attacker could exploit the issue

An attacker could reach this vulnerability by sending a specially crafted, forged JSON Web Token (JWT) to the application's authentication endpoint. The `validateAccessToken` function, which is intended to verify the token's signature, fails to do so, allowing the attacker to bypass authentication and gain unauthorized access. This could lead to full control over the application.

  • No authentication or special access needed.
  • Forged JWT sent to authentication endpoint.
  • Unauthenticated access and full control.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an unauthenticated attacker to bypass authentication and gain unauthorized access to the application by submitting a forged JSON Web Token (JWT). This could lead to unauthorized access to system functions and potentially sensitive information, depending on the application's design and the attacker's objectives.

  • Application access and functions.
  • Forged JWT token submission.
  • Unauthorized system access.

Priority actions

Operational Fix

Recommended remediation, mitigation, and detection steps

This critical vulnerability in bookcars' authentication bypass requires immediate attention from the platform or application owners. The first practical step is to identify all instances of bookcars, confirm their exposure and business criticality, and assign ownership for remediation planning.

  • App/Platform owners should own this issue.
  • Verify bookcars instances and exposure.
  • Plan and execute targeted remediation.

Frequently asked questions

What is the bookcars software used for?

Bookcars is a web-based application designed to manage vehicle rental and booking workflows. It utilizes JSON Web Tokens to handle user sessions and verify credentials as users navigate the platform to make reservations or manage bookings.

How does CVE-2026-36721 allow authentication bypass?

This flaw belongs to the CWE-347 class, which refers to improper verification of cryptographic signatures. Because the validateAccessToken function does not check these signatures, the system cannot verify that a token was issued by a trusted authority, allowing a forged JWT to be accepted as valid.

Do I need special access to trigger this vulnerability?

No special permissions are required. An attacker can exploit this by sending a crafted, forged token to the authentication endpoint. It is important to note that sending a legitimate, non-forged token or interacting with other application features unrelated to authentication does not trigger this specific defect.

Is my instance of bookcars at risk?

According to Halo Surface Signal, this vulnerability is likely to affect installations because bookcars is typically deployed as an internet-facing web service. Any instance reachable from the public network is a more significant concern than those restricted to internal, private segments.

How should I respond to this threat?

Begin by auditing your internal environment to create an inventory of all deployed bookcars instances. Once you have located these assets, determine their business criticality and verify whether they are exposed to the public internet, then prioritize them for an update or patching cycle to address the authentication logic.

References

Sources and related resources

Primary sources: NVD, CVE.org.

NVDPublished Modified