Exploited. On CISA's list since 2022-01-21.
SolarWinds Serv-U Improper Input Validation Vulnerability
CVE-2021-35247 · SolarWinds Serv-U · Published 2022-01-10
How bad would it be?
5.3 out of 10
CVSS rates it medium.
How likely is it to be used?
3.5%
Estimated chance of exploitation in the next 30 days, higher than 88% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1729 days ago (2022-02-04).
What CISA says to do
Apply updates per vendor instructions.
SolarWinds Serv-U versions 15.2.5 and earlier contain an improper input validation vulnerability that allows attackers to build and send queries without sanitization.
What the flaw is
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.
From the NVD.
Fixes and advisories
Learn this
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Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
CWE-20 · CISA KEV; NVD record: psirt@solarwinds.com. We have not selected a close learning match for this label.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.