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CVE-2021-35211 is a pre-authentication remote code execution vulnerability in the SSH implementation of SolarWinds Serv-U Managed File Transfer and Serv-U Secure FTP for Windows before 15.2.3 HF2. The flaw is triggered during handling of malformed SSH connection traffic prior to authentication. Analysis indicates Serv-U processes the SSH NEWKEYS message out of sequence and activates a partially initialized AES-CTR cipher context. Because the AES128-CTR context can be created before key material is fully initialized, subsequent decryption may use uninitialized data as a function pointer during OpenSSL AES-CTR processing, leading to attacker-controlled code execution. Exploitation is performed by connecting to the exposed SSH service and sending a malformed pre-auth request sequence. The issue has also been described as a remote memory escape vulnerability. Successful exploitation can cause Serv-U to spawn attacker-controlled subprocesses and may also generate access violation exceptions or crash the Serv-U process during exploitation attempts.
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No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
20 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A remote code execution vulnerability in SolarWinds Serv-U referenced as a prior, more severe Serv-U flaw for comparison with CVE-2026-28318.
A remote code execution vulnerability in SolarWinds Serv-U that was exploited as a zero-day for espionage and later by the Cl0p ransomware group.
A SolarWinds Serv-U remote code execution vulnerability that was exploited by both ransomware operators and a named threat actor in attacks against corporate networks.
A prior SolarWinds Serv-U vulnerability referenced as having been exploited by malicious actors (details not provided in the content).
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.