CVE-2021-35247: SolarWinds Serv-U Improper Input Validation Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 21 Jan 2022, 14 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 3.5%
EPSS score, percentile 89 of all scored records
- How severe?
- 4.3 Medium
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline 4 Feb 2022. Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- from 15.2.5 and previous versions to before 15.3
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: 4 February 2022.
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 15.2.5 and previous versions to before 15.3 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
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.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2021-35247 to its Known Exploited Vulnerabilities (KEV) catalog on 21 Jan 2022.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 4 Feb 2022.
- The CVE record was published on 7 Jan 2022, 14 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 4.3 (Medium), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 3.5% (percentile 89), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact partial.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
Description
Improper Input Validation Vulnerability in Serv-U
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
- CWE-20: Improper Input Validation
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 7 Jan 2022 | CVE record published |
| 21 Jan 2022 | Added to CISA KEV |
| 4 Feb 2022 | CISA due date for the required action |
| 21 Oct 2025 | CVE record last updated |
References
More exploited SolarWinds vulnerabilities
- CVE-2026-28318: SolarWinds Serv-U Uncontrolled Resource Consumption Vulnerability
- CVE-2025-26399: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability
- CVE-2025-40536: SolarWinds Web Help Desk Security Control Bypass Vulnerability
- CVE-2025-40551: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability
- CVE-2024-28987: SolarWinds Web Help Desk Hardcoded Credential Vulnerability
- CVE-2024-28986: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability