Ios XeOperating system · Cisco
CVE-2024-20309
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA vulnerability in auxiliary asynchronous port (AUX) functions of Cisco IOS XE Software could allow an authenticated, local attacker to cause an affected device to reload or stop responding. This vulnerability is due to the incorrect handling of specific ingress traffic when flow control hardware is enabled on the AUX port. An attacker could exploit this vulnerability by reverse telnetting to the AUX port and sending specific data after connecting. A successful exploit could allow the attacker to cause the device to reset or stop responding, resulting in a denial of service (DoS) condition.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceThis is a local authenticated vulnerability in Cisco IOS XE Software's auxiliary asynchronous port (AUX) functions. When flow control hardware is enabled on the AUX port, the software incorrectly handles specific ingress traffic. An attacker with local access can exploit this by reverse telnetting to the AUX port and sending crafted data, causing the device to reload or become unresponsive.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
Ios XeOperating system
= 3.2.0se= 3.2.1se= 3.2.2se= 3.2.3se= 3.3.0se= 3.3.0sq= 3.3.1se= 3.3.1sq= 3.3.2se= 3.3.3se= 3.3.4se= 3.3.5seCVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check IOS XE versionRun 'show version' and locate the version number in the outputAffected if The installed version matches one of these: 3.2.0se, 3.2.1se, 3.2.2se, 3.2.3se, 3.3.0se, 3.3.0sq, 3.3.1se, 3.3.1sq, 3.3.2se, 3.3.3se, 3.3.4se, or 3.3.5se
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Verify AUX port is enabledRun 'show running-config | include aux' or 'show line' to check if the AUX port is configured and activeAffected if The AUX port is present in the configuration and shows as active with a status other than 'disabled'
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Confirm flow control is enabled on AUX portRun 'show line aux 0' and examine the output for flow control settings; check the hardware flow control fieldAffected if Hardware flow control (RTS/CTS) is enabled on the AUX port (typically shown as 'flowcontrol hardware' in the line configuration)
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Check for reverse telnet access to AUX portRun 'show tcp' or examine running-config for lines starting with 'line aux 0' with 'transport input telnet' or 'transport output telnet'Affected if The AUX port is configured to accept telnet connections (transport input telnet or transport output telnet)
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Verify physical access exposureReview access control lists, physical security policies, and who has console/AUX port access rightsAffected if Multiple users or unauthenticated persons have potential physical or logical access to the AUX port
You are affected if your device runs an affected IOS XE version listed above AND has the AUX port enabled with hardware flow control configured AND allows telnet access to that port.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedApply the Cisco security patch for this vulnerability when available. If the AUX port is not required, disable it. Restrict physical and logical access to the AUX port to prevent local authenticated attackers from exploiting this issue.
Upgrade to IOS XE 3.2.4se or later in the 3.2.xse train (or migrate to a currently supported IOS XE train such as 16.x or 17.x as appropriate for your hardware platform)
- 1. Identify the current Cisco IOS XE version on the affected device using 'show version' command
- 2. Access the Cisco Security Advisory at sec.cloudapps.cisco.com for CVE-2024-20309 to confirm the exact fixed release for the 3.2.xse train
- 3. Plan an upgrade window as the device will require a reload after the IOS XE software upgrade
- 4. Backup the current device configuration using 'copy running-config startup-config' or 'archive config'
- 5. Download the fixed IOS XE release (typically 3.2.4se or later in the same train, or migrate to a supported train) from Cisco.com
- 6. Install the new IOS XE image using 'install add file' followed by 'install activate' and 'install commit' commands, or traditional ROMMON upgrade method
- 7. Verify the device reloads successfully and is running the patched version using 'show version'
- 8. Confirm the AUX port functionality is restored and the device no longer reloads when receiving specific traffic on the AUX port
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Ios Xe
Scoped from the published advisory
- Consultation2.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2024-20309 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2024-20309 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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