External risk intelligence

Perl Punk Session Cookie Forgery Vulnerability.

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-75870

This vulnerability affects a session management component in a web application framework. Session handling is a fundamental requirement for web applications, which are commonly deployed as public-facing services. Because the flaw involves forging session cookies, it is directly reachable via the standard public web interface of any application utilizing this framework.

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A security vulnerability in the Punk session management component of the Perl programming language could allow an attacker to forge session cookies. This occurs when the component is configured without a secret, leading to predictable session identifiers that attackers can then manipulate. At a high level, this could potentially allow unauthorized access or privilege escalation by impersonating legitimate users.

Session cookie forgery is possible without a secret.
It impacts user authentication and session integrity.
Confirm if your applications use this component.

Attack Path

How an attacker could exploit the issue

An attacker can forge session cookies for a web application by exploiting a misconfiguration in the Punk session management feature. This occurs when the application declares a session without providing a secret key. The system then defaults to an empty key, allowing an attacker to create a valid-looking cookie offline that the application will trust, potentially granting unauthorized access or privileges.

No prior access needed.
Empty session secret key.
Forged cookies grant access.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to forge session cookies when a session is declared without a secret. This occurs because the system defaults to an empty HMAC key, allowing any attacker to sign and verify cookies offline with custom contents.

User session data could be affected.
Attackers could forge cookies offline.
Unauthorized access to user roles may occur.

Operational Fix

Recommended remediation, mitigation, and detection steps

Application owners and platform teams are likely responsible for addressing this vulnerability, as it impacts session management within a web application framework. The first practical step is to identify all instances of the affected technology, confirm their exposure and criticality, and then determine the accountable owner to plan remediation.

Identify affected applications and owners.
Verify session cookie reachability and criticality.
Plan risk-based remediation or mitigation.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Punk framework in Perl?

Punk is a software component designed for Perl applications to manage user sessions. It provides the logic needed to track users as they move through a website, primarily by generating and verifying cookies that identify a specific session. Developers use it to handle the persistence of user data, such as login states or preferences, across multiple web requests.

How does CVE-2026-75870 allow session cookie forgery?

The vulnerability involves a weakness class identified as CWE-1394, which relates to the use of insufficient cryptographic keys. In this case, the Punk component fails to require a secret key for signing cookies. If no secret is defined, the system defaults to an empty string. This allows anyone to calculate the correct signature for a cookie offline, effectively tricking the application into accepting fabricated user data as legitimate.

Do I need a special trigger to exploit this flaw?

No complex preconditions are required. The vulnerability is triggered automatically if the application configuration omits a session secret. Crucially, the bug does not occur if a valid, non-empty secret key is properly configured; the system only falls back to the dangerous empty key when the developer neglects to provide one during the session declaration.

Is my application relevant according to Halo Surface Signal?

Halo Surface Signal indicates this is a high-relevance issue because session management is a core function of public-facing web services. Since the vulnerability is reachable through the standard web interface of any application using the affected framework, any service exposed to the internet that relies on Punk for session handling should be treated as a potential target for cookie forgery.

When should I take action for CVE-2026-75870?

You should begin by auditing your codebases to identify which applications utilize the Punk component. Verify whether your current session configurations include a strong, defined secret key. If you find instances missing this configuration, coordinate with your development team to implement a proper secret immediately to ensure session integrity and prevent unauthorized user impersonation.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.