Cyber Resilience

CVE-2026-18691

Published
11 August 2026
Modified
11 August 2026
CVSS Score v4 9.0
Click a component to see what it means
Raw vectorCVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/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:X
EPSS Score 0.0023 14th percentile
Risk Priority 38 floored blend · peak EPSS

Summary

CVE-2026-18691 is a critical-severity Algorithm Downgrade (CWE-757) vulnerability in Mongodb (inferred from references). Its CVSS base score is 9.0 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Downgrade Attack (T1689); ranked at the 14th 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-13 (Cryptographic Protection) and SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A04:2025 Cryptographic Failures

EU & UK References

Vulnerability Data

An issue in MongoDB Server's intra-cluster connection setup could allow a party with suitable network access to influence which authentication mechanism is used when one replica set member connects to another. Under certain conditions, this could cause the cluster's shared…

more

internal credential to be transmitted in a less-protected form, potentially allowing that credential to be recovered. If recovered, the credential could be used to authenticate as the internal superuser to nodes in the deployment.

CWE(s)
CWE-757

Related Threats

MITRE ATT&CK Enterprise Techniques

T1689 Downgrade Attack Defense Impairment
Adversaries may downgrade or use a version of system features that may be outdated, vulnerable, and/or does not support updated security controls.
attack.mitre.org →
T1600 Weaken Encryption Defense Impairment
Adversaries may compromise a network device’s encryption capability in order to bypass encryption that would otherwise protect data communications.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-2974Shared CWE-757
CVE-2025-59270Shared CWE-757
CVE-2026-32650Shared CWE-757
CVE-2024-38883Shared CWE-757
CVE-2025-36582Shared CWE-757
CVE-2026-55953Shared CWE-757
CVE-2026-4942Shared CWE-757
CVE-2025-10693Shared CWE-757
CVE-2026-2673Shared CWE-757
CVE-2026-1677Shared CWE-757

Affected Assets

Mongodb
—
inferred from references and description; NVD did not file a CPE for this CVE

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 7 hardening rules · 5 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V12.1.1
  • V12.2.1
  • V12.3.3
  • V17.2.2

Mitigating Controls (NIST 800-53 r5) AI

SC-13 Cryptographic Protection good match

Specifying and implementing required cryptography types directly precludes negotiation or acceptance of weaker algorithms.

SC-8 Transmission Confidentiality and Integrity partial match

Requiring protection of transmitted confidentiality and integrity forces selection of sufficiently strong negotiated algorithms rather than weaker ones.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-04 none match
prevents

PR.AA-04 addresses protection/verification of identity assertions in SSO/federation contexts while CWE-757 concerns protocol-level crypto algorithm negotiation, so the control neither prevents nor meaningfully mitigates the weakness.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect and block algorithm downgrade vulnerabilities before deployment.

A.8.21 Security of network services partial match
mitigates

Ensures network services use secure cryptographic parameters, reducing downgrade risk.

A.8.24 Use of cryptography partial match
prevents

Mandates use of strong, approved cryptographic algorithms, directly preventing downgrade to weaker ones.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC practices include selecting strong crypto algorithms during design and implementation.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify minimum cryptographic strength to avoid downgrades.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include enforcing strong algorithm selection in protocol design.

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 `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).

Windows 10 (1 rule)
  • V-220938 The LanMan authentication level must be set to send NTLMv2 response only, and to refuse LM and NTLM. prevents CWE-757
Windows 11 (1 rule)
  • V-253462 prevents CWE-757
Windows Server 2016 (1 rule)
  • V-225054 The LAN Manager authentication level must be set to send NTLMv2 response only and to refuse LM and NTLM. prevents CWE-757
Windows Server 2019 (1 rule)
  • V-205919 Windows Server 2019 LAN Manager authentication level must be configured to send NTLMv2 response only and to refuse LM and NTLM. prevents CWE-757
Windows Server 2022 (1 rule)
  • V-254475 prevents CWE-757

References