CVE-2026-33308VulnerabilityPublished 24 Mar 2026

CVE-2026-33308: airtower-luna mod_gnutls · Improper Certificate Validation

Affects airtower-luna mod_gnutlsSource CVE Database V5

Not known to be exploited · CVSS 6.8 Medium : upgrade to 0.13.0 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

6.8Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.13.0

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: None
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
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: None: There is no loss of integrity within 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 24 Mar 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 2026-10-25.

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 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.

What to do

Upgrade mod_gnutls and airtower-luna/mod_gnutls to 0.13.0.

Affected software

Product	Affected	Fixed in
airtower-lunamod_gnutls	Affected <0.13.0	Fixed in 0.13.0
GitHubairtower-luna/mod_gnutls`pkg:github/airtower-luna/mod_gnutls`Other threats	Affected <0.13.0	Fixed in 0.13.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade mod_gnutls to version 0.13.0 or later, which includes the fix enforcing proper Extended Key Usage validation. Review and enforce strict certificate issuance policies to ensure that client certificates are issued only by dedicated CAs or sub-CAs specifically for client authentication purposes. Configure the GnuTLSClientKeyPurpose option carefully if custom key purposes are required, ensuring they align with security policies. Audit existing client certificates to identify any that may be misused due to improper EKU settings and revoke or reissue them as necessary. Implement monitoring and logging of TLS client authentication attempts to detect anomalous usage patterns. Consider additional layers of authentication or authorization beyond TLS client certificates to reduce reliance on certificate EKU enforcement alone. Regularly review and test TLS configurations to ensure compliance with best practices and to detect potential misconfigurations.

Description

Mod_gnutls is a TLS module for Apache HTTPD based on GnuTLS. Prior to version 0.13.0, code for client certificate verification did not check the key purpose as set in the Extended Key Usage extension. An attacker with access to the private key for a valid certificate issued by a CA trusted for TLS client authentication but designated for a different purpose could have used that certificate to improperly access resources requiring TLS client authentication. Server configurations that do not use client certificates (`GnuTLSClientVerify ignore`, the default) are not affected. The problem has been fixed in version 0.13.0 by rewriting certificate verification to use `gnutls_certificate_verify_peers()`, and requiring key purpose id-kp-clientAuth (also known as `tls_www_client` in GnuTLS) by default if the Extended Key Usage extension is present. The new `GnuTLSClientKeyPurpose` option allows overriding the expected key purpose if needed (please see the manual for details). Behavior for certificates without an Extended Key Usage extension is unchanged. If dedicated (sub-)CAs are used for issuing TLS client certificates only (not for any other purposes) the issue has no practical impact.

Impact

This vulnerability can lead to unauthorized access to systems relying on TLS client authentication, potentially exposing sensitive data or services to attackers who possess a valid certificate private key issued for a different purpose. The confidentiality of protected resources is at risk, as attackers can impersonate legitimate clients without possessing a properly purposed certificate. Although the vulnerability does not affect server availability or data integrity directly, the breach of confidentiality can have significant operational and reputational consequences. Organizations using mod_gnutls versions prior to 0.13.0 with client certificate authentication enabled are at risk, especially if they do not segregate certificate issuance by purpose or rely on multi-purpose certificates. The lack of known exploits reduces immediate risk, but the vulnerability's nature makes it a candidate for targeted attacks in environments where client certificate authentication is critical.

CWE-295Improper Certificate Validation (opens in a new tab)
Base weaknessOWASP Top 10 A07:2025: Authentication Failures (opens in a new tab)
The product does not validate, or incorrectly validates, a certificate.
Architecture and Design · Implementation
Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
Implementation
If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
OWASP Cheat Sheets
Transport Layer Protection (opens in a new tab)
TLS Cipher String (opens in a new tab)
OWASP Authentication (opens in a new tab)
OWASP ASVS 4.0.3
V9.2.1 (opens in a new tab)
V1.9.2 (opens in a new tab)
V2.8.5 (opens in a new tab)
Attack patterns
Creating a Rogue Certification Authority Certificate (opens in a new tab)
Signature Spoofing by Improper Validation (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/airtower-luna/mod_gnutls/security/advisories/GHSA-hm2g-m958-8qgh (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 24 Mar 2026, 14:31 UTC

WeaknessesCWE-295

Technical details

References

Community reviews

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