Cyber Resilience

CVE-2026-62911

Auth Bypass in Microsoft Exchange Server 2016 … 2019

Auth Bypass
Published
11 August 2026
Modified
13 August 2026
Patch / advisory
View advisory
CVSS Score v3.1 8.0
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
EPSS Score 0.0095 59th percentile
Risk Priority 60 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-62911 is a high-severity Authentication Bypass by Capture-replay (CWE-294) vulnerability in Microsoft Exchange Server. Its CVSS base score is 8.0 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Network Sniffing (T1040); ranked in the top 41% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SC-23 (Session Authenticity) and SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

Authentication bypass by capture-replay in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.

CWE(s)
CWE-294

Related Threats

MITRE ATT&CK Enterprise Techniques

T1040 Network Sniffing Credential Access
Adversaries may passively sniff network traffic to capture information about an environment, including authentication material passed over the network.
attack.mitre.org →
T1550.003 Pass the Ticket Lateral Movement
Adversaries may “pass the ticket” using stolen Kerberos tickets to move laterally within an environment, bypassing normal system access controls.
attack.mitre.org →
T1550.004 Web Session Cookie Lateral Movement
Adversaries can use stolen session cookies to authenticate to web applications and services.
attack.mitre.org →
T1557 Adversary-in-the-Middle Credential Access
Adversaries may attempt to position themselves between two or more networked devices using an adversary-in-the-middle (AiTM) technique to support follow-on behaviors such as [Network Sniffing](https://attack.
attack.mitre.org →
T1021 Remote Services Lateral Movement
Adversaries may use [Valid Accounts](https://attack.
attack.mitre.org →
T1021.002 SMB/Windows Admin Shares Lateral Movement
Adversaries may use [Valid Accounts](https://attack.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-53786Same product: Microsoft Exchange Server
CVE-2025-53782Same product: Microsoft Exchange Server
CVE-2025-59249Same product: Microsoft Exchange Server
CVE-2025-33051Same product: Microsoft Exchange Server
CVE-2026-42897Same product: Microsoft Exchange Server
CVE-2026-55008Same product: Microsoft Exchange Server
CVE-2026-65813Same product: Microsoft Exchange Server
CVE-2025-59248Same product: Microsoft Exchange Server
CVE-2026-47631Same product: Microsoft Exchange Server
CVE-2026-45583Same product: Microsoft Exchange Server

Affected Assets

microsoft
exchange server
2016, 2019
microsoft
exchange server subscription edition
≤ 15.02.2562.046

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V10.4.16
  • V10.5.1

Mitigating Controls (NIST 800-53 r5) AI

SC-23 Session Authenticity good match

Session authenticity mechanisms directly stop replay of captured authentication traffic by enforcing freshness or cryptographic binding.

SC-8 Transmission Confidentiality and Integrity good match

Transmission integrity (with anti-replay) stops captured messages from being accepted as valid later.

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 mostly match
prevents

Protecting and verifying identity assertions prevents replay of captured authentication material.

PR.DS-02 mostly match
prevents

Encryption and integrity protections for data-in-transit directly block capture-replay of credentials or tokens.

DE.CM-01 partial match
prevents

Network monitoring may detect anomalous replays after the fact but does not prevent the design flaw.

PR.AA-03 partial match
prevents

Strong authentication methods can reduce replay risk but do not inherently address captured messages.

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.8.24 Use of cryptography mostly match
prevents

Cryptographic protections (e.g., nonces, timestamps, message authentication codes) make captured authentication messages unusable for replay.

A.8.5 Secure authentication mostly match
prevents

Secure authentication mechanisms directly prevent replay attacks by requiring fresh, non-replayable credentials or tokens.

A.8.20 Networks security partial match
mitigates

Network security controls such as encryption and integrity protection reduce the feasibility of capturing and replaying authentication traffic.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate replay-resistant authentication designs, but the control itself does not prescribe the technical measures.

References