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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 processing of malformed SSH handshake traffic. Analysis indicates Serv-U can process an SSH NEWKEYS message out of sequence, prematurely activating a partially initialized AES-CTR cipher context. Because the AES128-CTR context may be created before key material is fully initialized, subsequent decryption can dereference uninitialized data as a function pointer, leading to attacker-controlled code execution. The vulnerable path involves Serv-U SSH message parsing and OpenSSL AES-CTR handling during pre-auth connection setup. Exploitation has been observed in the wild and can result in Serv-U spawning attacker-controlled subprocesses.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
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.
19 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.