CVE-2024-20390 Overview
CVE-2024-20390 is a denial-of-service vulnerability in the Dedicated XML Agent feature of Cisco IOS XR Software. An unauthenticated, remote attacker can render XML TCP listen port 38751 unreachable by sending a sustained stream of crafted XML traffic. The root cause is insufficient error validation of ingress XML packets [CWE-940]. The condition persists while attack traffic continues, disrupting management and orchestration workflows that depend on the XML Agent interface.
Critical Impact
Unauthenticated attackers with network access to TCP port 38751 can disable the Cisco IOS XR XML management interface, impacting network automation and provisioning operations.
Affected Products
- Cisco IOS XR Software with the Dedicated XML Agent feature enabled
- Devices exposing XML TCP listen port 38751
- See the Cisco Security Advisory for the fixed release matrix
Discovery Timeline
- 2024-09-11 - CVE-2024-20390 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-20390
Vulnerability Analysis
The Dedicated XML Agent in Cisco IOS XR exposes an XML-based management interface on TCP port 38751. This interface accepts XML documents used for device configuration and operational queries. The vulnerability arises when the agent processes malformed or unexpected XML input without adequate error validation. A sustained stream of crafted XML packets exhausts the agent's ability to service legitimate connections. The affected port becomes unreachable for the duration of the attack, though the underlying device continues to forward traffic.
The issue is classified under [CWE-940] Improper Verification of Source of a Communication Channel, reflecting the agent's failure to reject or gracefully handle malformed ingress traffic. Exploitation does not require authentication, credentials, or user interaction. Only network reachability to port 38751 is required.
Root Cause
The Dedicated XML Agent lacks proper error validation on incoming XML packets. When it receives sustained malformed input, its parser fails to recover cleanly, blocking new connections to port 38751.
Attack Vector
An attacker sends a continuous stream of crafted XML traffic to TCP port 38751 on a reachable IOS XR device. The attack requires network-adjacent or routed access to the management interface. Service impact is limited to the XML Agent listener and persists only while attack traffic continues. Refer to the Cisco Security Advisory for exploitation constraints and confirmed fixed releases.
Detection Methods for CVE-2024-20390
Indicators of Compromise
- Sustained inbound TCP sessions to port 38751 from untrusted or unexpected sources
- Failed XML Agent connection attempts from legitimate management stations coinciding with high inbound traffic to port 38751
- Repeated malformed XML payloads observed on the management plane
Detection Strategies
- Monitor Cisco IOS XR syslog and process logs for XML Agent restarts, parser errors, or connection failures
- Deploy network intrusion detection signatures that flag high-rate or malformed XML traffic destined for TCP port 38751
- Correlate NetFlow or IPFIX records for anomalous session counts targeting the management plane
Monitoring Recommendations
- Alert on any external source reaching TCP port 38751; the management plane should not be exposed to untrusted networks
- Track availability of the XML Agent through synthetic health checks from authorized NMS hosts
- Baseline expected management traffic volumes and alert on sustained deviations
How to Mitigate CVE-2024-20390
Immediate Actions Required
- Restrict access to TCP port 38751 using infrastructure access control lists (iACLs) and control plane policing (CoPP) to permit only trusted management hosts
- Disable the Dedicated XML Agent on devices that do not require it
- Review the Cisco Security Advisory and plan upgrades to a fixed IOS XR release
Patch Information
Cisco has published fixed software releases addressing CVE-2024-20390. Consult the vendor advisory to identify the specific fixed train for your platform and IOS XR version. Apply the patch through standard change-management procedures and validate XML Agent functionality after upgrade.
Workarounds
- Apply iACLs on device ingress interfaces to block untrusted access to TCP port 38751
- Configure CoPP policies to rate-limit traffic destined for the XML Agent
- Segregate management traffic onto a dedicated out-of-band network unreachable from user or internet-facing segments
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
