CVE-2026-28318

SolarWinds Serv-U, an FTP and managed-file-transfer server, contains an uncontrolled resource consumption flaw (CWE-400) that allows an unauthenticated remote attacker to exhaust the service's resources. It is triggered by sending specially crafted POST requests with the Content-Encoding: deflate header, which crashes the Serv-U service. An attacker gains denial of service — file transfer operations stop until the service is restarted — and the available data indicates no remote code execution or data exposure. Any organization running Serv-U, typically enterprises using it as an internal or internet-facing file transfer endpoint, is affected; the available advisories do not specify affected version ranges. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-06-05, signaling exploitation in the wild, and EPSS estimates a 40% probability of exploitation within 30 days (99th percentile), though CVSS scoring is pending and no public proof-of-concept is known.

What to do: Inventory all Serv-U deployments and apply SolarWinds' mitigation per vendor instructions, or discontinue use of the product if mitigations are unavailable, as required by the KEV listing (federal agencies must follow BOD 22-01 timelines). As an interim mitigation, block or normalize POST requests carrying the Content-Encoding: deflate header at a WAF or reverse proxy and restrict Serv-U's internet exposure. Monitor the Serv-U service for crashes, since successful exploitation takes it down until it is restarted.