iOSOperating system · Cisco

CVE-2024-20433

HIGH · 7.5 CVSS v3.1 Published 2024-09-25

Mitigation only

No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.

See remediation →

84/100

Remediation priority · High

Remotely reachable No privileges Zero-click

Official description

NVD · unedited

A vulnerability in the Resource Reservation Protocol (RSVP) feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to a buffer overflow when processing crafted RSVP packets. An attacker could exploit this vulnerability by sending RSVP traffic to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition.

Technical summary

dbcve analysis · high confidence

A buffer overflow vulnerability exists in the Resource Reservation Protocol (RSVP) implementation of Cisco IOS and IOS XE Software. An unauthenticated remote attacker can exploit this by sending specially crafted RSVP packets to an affected device, triggering the overflow and causing an unexpected reload resulting in denial of service.

MitigationApply the Cisco IOS/IOS XE software update provided by Cisco to address this vulnerability. If RSVP is not required in the environment, consider disabling it or filtering RSVP traffic at network boundaries to reduce attack surface.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions

NVD · CPE data

iOSOperating system

Affected:= 12.0$24$s= 12.0$24$s1= 12.0$24$s2= 12.0$24$s2a= 12.0$24$s2b= 12.0$24$s3= 12.0$24$s4= 12.0$24$s4a= 12.0$24$s5= 12.0$24$s6= 12.0$25$s= 12.0$25$s1

Ios XeOperating system

Affected:= 3.3.0sg= 3.3.1sg= 3.3.2sg= 3.4.0sg= 3.4.1sg= 3.4.2sg= 3.4.3sg= 3.4.4sg= 3.4.5sg= 3.4.6sg= 3.4.7sg= 3.4.8sg

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify the installed Cisco IOS or IOS XE version

Execute 'show version' on the device CLI and locate the version string in the output (for IOS XE, look for version like 3.X.XSG; for IOS, look for version like 12.0(24)s through 12.0(25)s1)

Affected if The displayed version matches one of the affected versions listed in the CVE (12.0(24)s through 12.0(25)s1 for iOS, or 3.3.0sg through 3.4.8sg for IOS XE)
Verify whether RSVP protocol is enabled

Execute 'show ip rsvp' or 'show rsvp' in the device CLI to check RSVP status and configuration

Affected if RSVP is enabled and showing active sessions or interfaces with RSVP configured
Check RSVP interface configuration

Execute 'show running-config | include rsvp' or 'show ip interface' to list interfaces with RSVP enabled

Affected if Any interface is configured with RSVP (rsvp command present in interface configuration)
Determine network exposure to RSVP traffic

Review interface IP addressing and access lists using 'show ip interface' and 'show access-lists' to determine if RSVP traffic (port 3638/UDP) can reach the device from untrusted networks

Affected if RSVP is enabled and the device has reachable interfaces without proper filtering of UDP port 3638

The device is affected if it runs a Cisco IOS version between 12.0(24)s and 12.0(25)s1 or an IOS XE version between 3.3.0SG and 3.4.8SG, and RSVP protocol is enabled and reachable from untrusted networks.

Generated from the published advisory. Verify against your own configuration.

Remediation

dbcve · scoped

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

Apply the Cisco IOS/IOS XE software update provided by Cisco to address this vulnerability. If RSVP is not required in the environment, consider disabling it or filtering RSVP traffic at network boundaries to reduce attack surface.

Recommended fix Moderate confidence

Obtain the specific fixed release from Cisco security advisory; upgrade from affected 12.0(24)s variants to a later iOS release, and from affected 3.3.xsg/3.4.0sg IOS XE variants to a fixed IOS XE release as specified in the Cisco advisory

1. Identify the exact Cisco IOS or IOS XE version currently running on the affected device using 'show version' command
2. Consult the official Cisco security advisory on sec.cloudapps.cisco.com for this CVE to obtain the specific fixed software releases
3. Download the appropriate fixed Cisco IOS or IOS XE software release for your device model from the Cisco Software Center
4. Verify the fix is available for your specific device model before upgrading
5. Plan a maintenance window as the device will need to be reloaded after the upgrade
6. Back up the current device configuration before proceeding
7. Upgrade the Cisco IOS/IOS XE software using the appropriate method (TFTP, USB, etc.) with command: 'archive download-sw /overwrite /reload tftp://<server>/<image>
8. After upgrade, verify the device has reloaded and is functioning normally

Caveat Review Cisco release notes for your target version for any feature changes or configuration requirements that may differ from the affected versions

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in iOS Scoped from the published advisory

Consultation6.0 h
Implementation4.0 h
Testing8.0 h
Review / QA4.0 h

22.0 hours of engineering $3,840

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Scan for this in your stack

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References

Primary sources

sec.cloudapps.cisco.comVendor Advisory
nvd.nist.govNVD record

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2024-20433 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2024-20433?

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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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsA vendor remedy is published

Severity 7.5 High

Exploit likelihood EPSS, next 30 days 0.6%

Affects: iOS

Remediation

A high-priority fix

Fix this in iOS 22 hrs · Moderate

Typical engagement from $3,840

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2024-20433 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

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.

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.

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.

CVSS 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.

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.

Check your environment

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.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

Affected products & versions

CVSS breakdown

Am I affected?

Remediation

References