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Microsoft Exchange Server Elevation of Privilege Vulnerability

Not in CISA KEVPublic exploit codeCVE-2026-62911CWE-294

Not confirmed exploited. 1 of 8 rule sources name it. 1 public exploit repo.

Edge rules
1/8
Our test
No exploit yet
CVSS
8.0
EPSS
0.7% Top 47%
Posts, 14d
12026-10-20: 0 posts2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 1 posts
Published
2026-08-11

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

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AI · answers from this page
Ask about CVE-2026-62911: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 3.1
High · 8.0 / 10

Exploitable over the network, with low privileges and user interaction, leading to full loss of confidentiality, integrity and availability.

Over the internetAny user loginNeeds a user to actWorks reliablyFull compromise
How the score is built8 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo special conditions are needed; the attack works reliably.
    Low
  • Privileges requiredThe attacker needs an ordinary user account.
    Low
  • User interactionA user has to do something first, such as open a file or click a link.
    Required
  • ScopeThe damage stays within the vulnerable component.
    Unchanged
  • Confidentiality impactAn attacker can read all data the affected component holds, or the most sensitive parts of it.
    High
  • Integrity impactAn attacker can change any data or files the affected component protects.
    High
  • Availability impactAn attacker can take the component down completely or keep it from serving anyone.
    High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Also in the vector: Exploit code maturity: Unproven · Remediation level: Official fix · Report confidence: Confirmed

CISA's assessmentSSVC, from the CVE record
ExploitationProof of concept

Public exploit code or a detailed write-up exists, but CISA has not seen attacks.

AutomatableNo

At least one step needs hands-on work, which slows mass attacks.

Technical impactTotal

A successful attack gives full control over the affected software or all of its data.

Public exploits

1 found
0 Metasploit0 Exploit-DB0 Scanner template1 GitHub PoCs

No exploit in Exploit-DB or Metasploit, and no scanner template. That lowers, but doesn't remove, the chance of mass exploitation.

Links are to third-party code: never run it outside an isolated lab.

Timeline

  1. 2026-08-11
    CVE published
    CVE List
  2. 2026-10-21
    F5 ships a rule
    Microsoft Exchange MRSProxy Authentication Bypass
  3. 2026-11-02
    First public exploit repository
    c5z54/cve-2026-62911-poc: CVE-2026-62911 — Exchange MRSProxy Pre-Auth RCE PoC | Scanner + Exploit | NTLM Relay → Webshell → SYSTEM
  4. 2026-11-02
    First social mention we saw

Social

2026-10-20: 0 posts2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 1 posts

Exploit repos · unvetted, don't run

  • c5z54·

    c5z54/cve-2026-62911-poc: CVE-2026-62911 — Exchange MRSProxy Pre-Auth RCE PoC | Scanner + Exploit | NTLM Relay → Webshell → SYSTEM

    ★ 1View on GitHub

Vendor statements

Quoted
CloudflareWAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Each row gives the rule ID and its default action. The feed starts in January 2025, so older rules are missing.

AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Google names few CVEs: the release notes start in May 2024 and the rules reference lists CVEs without dates. Its cve-canary rules are opt-in.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2026-10-21, 71 days after the CVE was published.

2026-10-21New rule200013238Source
Added: signature 200013238 "Microsoft Exchange MRSProxy Authentication Bypass" (Authentication/Authorization Attacks, risk High), systems: Outlook Web Access. References: CVE-2026-62911.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.