VulnerabilityPublished 22 Aug 2026Updated 25 Aug 2026

CVE-2026-75870: CVE-2026-75870 affects Punk · Use of Default Cryptographic Key

Source CVE Database V5

Not known to be exploited · CVSS 9.1 Critical.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

9.1Critical

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 42% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-3679-xr9w-9625

What to do

AI-suggested

Until a fix is available, ensure that a non-empty secret is explicitly configured for sessions to avoid defaulting to an empty HMAC key. Avoid deploying Punk versions before 0.18 without proper secret configuration.

Description

CVE-2026-75870 affects Punk versions before 0.18 for Perl, where session cookies can be forged due to the use of an empty default HMAC key when no secret is provided. The session mechanism does not enforce or warn about the absence of a secret, resulting in signing and verification with a zero-length HMAC-SHA256 key. This allows an attacker who understands the cookie format to create valid session cookies with arbitrary contents such as user identifiers or roles without detection.

Impact

An attacker can create forged session cookies that the application will accept as valid, potentially impersonating users or escalating privileges. This compromises confidentiality and integrity of session data but does not affect availability. The vulnerability has a CVSS score of 9.1 (critical), indicating a high impact on confidentiality and integrity without requiring privileges or user interaction.

Summary

This vulnerability arises because the Punk session keyword does not require a secret key and defaults to an empty string for the HMAC key if none is provided. Consequently, session cookies are signed and verified using a zero-length HMAC-SHA256 key, enabling an attacker to forge session cookies offline. The forged cookies appear valid and are accepted by the application, potentially allowing unauthorized access or privilege escalation.

CWE-1394Use of Default Cryptographic Key (opens in a new tab)
Base weakness
The product uses a default cryptographic key for potentially critical functionality.
Requirements
Prohibit use of default, hard-coded, or other values that do not vary for each installation of the product - especially for separate organizations.
Architecture and Design
Force the administrator to change the credential upon installation.
Installation · Operation
The product administrator could change the defaults upon installation or during operation.
OWASP ASVS 4.0.3
V2.8.5 (opens in a new tab)
V2.8.4 (opens in a new tab)
V9.2.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 10 Sep 2026, 14:49 UTC

WeaknessesCWE-1394

Technical details

References

Community reviews

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