Veeam Patches CVE-2025-23121: Critical RCE Bug Rated 9.9 CVSS in Backup & Replication

Veeam Backup & Replication contains a deserialization of untrusted data flaw (CWE-502) that allows remote code execution. Per the CVSS vector (AV:N/AC:L/PR:L/UI:N), the attack is network-reachable, straightforward to execute, and requires only low-privilege credentials — a regular domain user — with no user interaction; the vendor description states it yields RCE 'for domain users'. An attacker who obtains or already holds any domain-user account that can reach the backup server gains code execution with high confidentiality, integrity and availability impact, a foothold that is especially dangerous in backup infrastructure because those servers often hold credentials for large parts of the estate and are prime ransomware targets. Any organization running Veeam Backup & Replication is potentially affected. Veeam has released a fix (reported alongside its patch for the related CVE-2025-23121, rated 9.9, in the same product); a public technical write-up/PoC from watchTowr exists, the flaw is not yet in CISA's KEV, and EPSS assigns a 24% probability (98th percentile) of exploitation within 30 days.

Do: Upgrade Veeam Backup & Replication to the patched release specified in Veeam's security advisory; if you already applied the fix for the related CVE-2025-23121 (CVSS 9.9), verify you are on the newest build, as this flaw was disclosed alongside that patch. Restrict network access to backup infrastructure, review which domain accounts can reach the B&R server, and monitor for exploitation attempts given the public PoC and elevated EPSS score.

CVE-2025-23121 is a code-injection vulnerability (CWE-94) in Veeam Backup & Replication that allows an authenticated domain user to execute arbitrary code on the Backup Server over the network. An attacker triggers it by sending a crafted request to the backup server's network-facing components using valid, low-privileged domain credentials, with no user interaction required. Successful exploitation yields full remote code execution with high impact on confidentiality, integrity and availability of the backup server (CVSS 3.1: 8.8 per the vector provided, though some coverage lists a 9.9 score). Any organization running Veeam Backup & Replication is affected, particularly environments where many or low-privilege domain accounts can reach the backup server. As of this writing it is not in CISA KEV and no public PoC is known, but the EPSS of 22.2% (98th percentile) indicates an elevated probability of exploitation within the next 30 days, and Veeam has shipped a fix.

Do: Upgrade Veeam Backup & Replication to the latest patched release per Veeam's security advisory for CVE-2025-23121. In the meantime, restrict which domain accounts can authenticate to the Backup Server, ensure the server is not exposed to the public internet, and audit for unusual process execution or network connections from backup infrastructure. Given the high EPSS score, prioritize patching and monitor Veeam/Kev feeds for signs of in-the-wild exploitation.

A vulnerability allowing local system users to modify directory contents, allowing for arbitrary code execution on the local system with elevated permissions.