CVE-2024-20509Network attack vector

Session hijacking via predictable authentication handlers

Published Oct 2, 2024 · Updated Jun 4, 2025

Race condition in the AnyConnect VPN server in Cisco Meraki MX Firmware allows remote attackers to hijack sessions or deny connections. Authentication handlers have insufficient entropy, and concurrent authentication processing permits a correctly guessed handler in crafted HTTPS requests to be claimed. Cisco AnyConnect VPN must be enabled; successful exploitation takes over one target user's VPN session or blocks that user from connecting.

CVSS severity5.8
Medium
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Race condition in the AnyConnect VPN server in Cisco Meraki MX Firmware allows remote attackers to hijack sessions or deny connections. Authentication handlers have insufficient entropy, and concurrent authentication processing permits a correctly guessed handler in crafted HTTPS requests to be claimed. Cisco AnyConnect VPN must be enabled; successful exploitation takes over one target user's VPN session or blocks that user from connecting.

The record

CVE
CVE-2024-20509
Published
Oct 2, 2024
Updated
Jun 4, 2025
Vendor
ClamAV
Product
Cisco Meraki MX Firmware
Classifications
CWE-362, T1499, T1563
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 2, 2024CVE publishedPublication date reported by the CVE source.
  2. Jun 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=-10
  2. Affected versionversion=-16-2
  3. Affected versionversion=-16-3
  4. Affected versionversion=-16-4
  5. Affected versionversion=-16-5
  6. Affected versionversion=.16.6
  7. Affected versionversion=-3
  8. Affected versionversion=-6
  9. Affected versionversion=-7
  10. Affected versionversion=-8
  11. Affected versionversion=-9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Meraki MX Firmwareversion=-10; version=-16-2; version=-16-3; version=-16-4; version=-16-5; version=.16.6; version=-3; version=-6; version=-7; version=-8; version=-9

Published CVSS scores

5.8CiscoCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
T1499Endpoint Denial of Service
T1563Remote Service Session Hijacking

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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