IBM MQ’s .NET client contains a XML External Entity injection flaw in its RFH2 folder parsing logic. When a client supplies crafted XML, the parser can resolve external entities, allowing an authenticated attacker to read arbitrary files from the client machine or trigger a limited denial of service by manipulating the parsing routine. This weakness maps to CWE‑611 and requires the attacker to have valid MQ credentials to exploit.

The vulnerability affects IBM MQ .NET client versions 9.1.0.0 through 9.1.0.37, 9.2.0.0 through 9.2.0.43, 9.3.0.0 through 9.3.0.41, 9.3.0.0 through 9.3.5.1 in the CD distribution, 9.4.0.0 through 9.4.0.25, 9.4.0.0 through 9.4.5.1 in the CD distribution, and 10.0.0.0. IBM publishes cumulative security updates that address this issue: 9.1.0.38 for 9.1 LTS, 9.2.0.44 for 9.2 LTS, 9.3.0.42 for 9.3 LTS, 9.4.0.26 for 9.4 LTS, and the 10.0.0.5 upgrade for the 10.0.0.0 release.

With a CVSS score of 7.1, the flaw is considered high severity. Exploitation requires an authenticated network connection to the MQ server and the use of the desktop .NET client; it does not provide remote code execution. The EPSS score is not available, and the vulnerability is not listed in CISA’s KEV catalog, implying no known widespread exploitation yet. The attack path would involve the attacker sending malicious XML over the network to the client, triggering the vulnerable parser and consequently reading files or causing a limited denial of service.