Raw vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). EPSS, Forum of Incident Response and Security Teams (FIRST), epss.first.org. Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-121638 is a critical-severity Improper Certificate Validation (CWE-295) vulnerability in Watchguard (inferred from references). Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Masquerading (T1036); ranked at the 22th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SC-17 (Public Key Infrastructure Certificates) and SC-23 (Session Authenticity) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-116931
Vulnerability Data
An Improper Certificate Validation vulnerability in WatchGuard AuthPoint Gateway allows an attacker with an on-path network position to intercept and modify communications between the AuthPoint Gateway and local authentication providers.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
MITRE ATT&CK v20.0
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 12 hardening rules · 3 OS baselines
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Mitigating Controls (NIST 800-53 r5)
Our mappings, made for this CVE.
PKI certificate issuance and acquisition under an approved policy establishes the trusted roots and processes needed for correct validation.
Protecting session authenticity depends on cryptographic mechanisms whose trust depends on correct certificate validation.
Requiring confidentiality and integrity protection of transmitted data drives use of properly validated certificates in protocols such as TLS.
Mitigating Controls (NIST CSF 2.0)
Our mappings, derived directly from the weakness types (CWEs) cited in the NVD entry via our CWE→CSF cross-walk — links open the control.
Certificate-based authentication of users/services/hardware directly depends on correct validation.
Proper certificate validation is a core mechanism for protecting data-in-transit confidentiality and integrity.
Secure development practices explicitly include implementing correct certificate validation logic.
Assessing authenticity/integrity of acquired software often relies on code-signing certificate validation.
Identity assertions conveyed via certificates require validation to be verified.
Mitigating Controls (ISO/IEC 27001:2022 Annex A)
Our mappings, derived directly from the weakness types (CWEs) cited in the NVD entry via our CWE→ISO cross-walk — links open the control.
A.8.29's programme (code review, static analysis, penetration testing) reaches most CWE-295 instances as first-party code defects — missing SSL_get_verify_result calls, disabled validation flags, unchecked hostname matching — all visible in source or observable at runtime by presenting an invalid certificate; the bounded remainder is instances where certificate pinning makes post-implementation testing difficult (noted in the CWE's Modes of Introduction) and validation logic buried inside third-party libraries that the developer's source-level review does not read, though pen-testing catches the symptom in many of those.
Training developers on proper TLS/certificate validation APIs and the importance of chain, hostname, and revocation checks reduces some instances of CWE-295, but the weakness is a specialized implementation defect where even trained developers make mistakes (e.g., skipping SSL_get_verify_result, accepting self-signed certs, using curl -k), so the effect is a minority one — consistent with the A.6.3 vs CWE-598 anchor at the same rung.
Requiring issuance and validation of public-key certificates under an approved policy reduces the chance that certificates with improper validation will be trusted.
A.8.28 mandates secure coding practices (standards, peer review, training, prohibition of insecure techniques) that reduce improper certificate validation defects, but the mechanism is human practice and is fallible; the clause's declared ceiling on this verb is `partial`, matching the same-clause grades against CWE-79 and CWE-502.
A.8.30 carries its effect through the secure-development practices its contract requires of the supplier (8.25 to 8.29), so it reduces ordinary software implementation weaknesses like improper certificate validation the way those practices do, at `partial` -- the same reasoning the owner applied to A.8.30 -> CWE-134, and the clause carries a declared ceiling of `partial` on this verb.
A.8.8's reach is DISCLOSURE — it sees only instances that carry a vendor-published flaw. CWE-295 does surface as CVEs (Apple goto fail, Go framework, router firmware, etc.), so the disclosed share is found, but the bulk of certificate-validation defects live in custom first-party code with no published advisory, which is outside A.8.8's reach and belongs to A.8.29.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over our cross-walk; rows rated `none` are excluded, and each rule says how its mapping was checked.
Definition changed on 29 October 2026. Until then this section listed every rule rated above none, partial included. From that date it lists rules whose mapping is rated full or mostly and checked at llm_unverified or higher; partial mappings show when you ask.
Oracle Linux 8 (3 rules)
- V-248574 YUM must be configured to prevent the installation of patches, service packs, device drivers, or OL 8 system components that have not been digitally signed using a certificate that is recognized and approved by the organization. blocks CWE-295
- V-248531 OL 8, for PKI-based authentication, must validate certificates by constructing a certification path (which includes status information) to an accepted trust anchor. blocks CWE-295
- V-248575 OL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. blocks CWE-295
RHEL 7 (2 rules)
- V-204447 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. blocks CWE-295
- V-204448 The Red Hat Enterprise Linux operating system must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. blocks CWE-295
RHEL 8 (2 rules)
- V-230264 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components from a repository without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. blocks CWE-295
- V-230265 RHEL 8 must prevent the installation of software, patches, service packs, device drivers, or operating system components of local packages without verification they have been digitally signed using a certificate that is issued by a Certificate Authority (CA) that is recognized and approved by the organization. blocks CWE-295