Security Resilience

CVE-2021-35247

Solarwinds Serv-U ≤ 15.3

CISA KEVActive ExploitationEUVD Exploited
Published
10 January 2022
Modified
27 October 2025
KEV Added
21 January 2022
Patch / advisory
CVSS Score v3.1 4.3
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
EPSS Score 0.035 89th percentile
Risk Priority 75 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2021-35247 is a medium-severity Improper Input Validation (CWE-20) vulnerability in Solarwinds Serv-U. Its CVSS base score is 4.3 (Medium).

Operationally, ranked in the top 11% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

The vulnerability in CVE-2021-35247 is improper input validation affecting the web login screen's LDAP authentication mechanism in SolarWinds Serv-U. The component failed to sufficiently sanitize characters submitted during authentication, although the vendor notes that downstream LDAP servers ignored the improper input and no further impact was observed in practice. The issue is tracked under CWE-20 with a CVSS 3.1 score of 4.3.

An unauthenticated attacker can exploit the flaw over the network by supplying crafted input to the login interface, which requires user interaction such as clicking a malicious link. Successful exploitation yields limited integrity impact while leaving confidentiality and availability unaffected.

SolarWinds Serv-U release notes for version 15.3 and the associated security advisory state that the input mechanism now performs additional validation and sanitization. The vendor recommends that all customers schedule an update to the latest Serv-U version to ensure proper validation regardless of LDAP server behavior. The vulnerability is listed in the CISA Known Exploited Vulnerabilities catalog.

OWASP Top 10 for Web (2025)

EU & UK References

Vulnerability Data

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…

more

improper characters. To insure proper input validation is completed in all environments. SolarWinds recommends scheduling an update to the latest version of Serv-U.

CWE(s)
KEV Date Added
21 January 2022

Related Threats

CVEs Like This One

CVE-2023-40053Same product: Solarwinds Serv-U
CVE-2021-35211Same product: Solarwinds Serv-Uboth on KEV
CVE-2024-28995Same product: Solarwinds Serv-Uboth on KEV
CVE-2024-45714Same product: Solarwinds Serv-U
CVE-2024-28073Same product: Solarwinds Serv-U
CVE-2024-45711Same product: Solarwinds Serv-U
CVE-2023-40060Same product: Solarwinds Serv-U
CVE-2023-35179Same product: Solarwinds Serv-U
CVE-2023-23841Same product: Solarwinds Serv-U
CVE-2024-28072Same product: Solarwinds Serv-U

Affected Assets

solarwinds
serv-u
≤ 15.3

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-20

Security testing and developer training directly verify and enforce proper input validation, reducing exploitability of injection and malformed-data weaknesses.

addresses: CWE-20

Security testing and evaluation at multiple SDLC stages directly detects missing or flawed input validation, with the required remediation process ensuring fixes are applied.

addresses: CWE-20

Directly implements checks on information inputs to reject invalid data before processing.

addresses: CWE-20

Spam protection mechanisms perform filtering and detection on inbound/outbound messages, directly compensating for missing or weak input validation of unsolicited content.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

blocks

A.8.25 mandates security requirements, secure coding guidelines, checkpoints, testing (incl. code scans) and developer training in the SDLC, which reaches a slice of input validation defects but leaves the majority (incomplete enforcement, second-order inputs, parser differentials, post-validation canonicalization) unaddressed as in the SA-3 and A.8.28 anchors.

blocks

Mandating input controls that include integrity checks and input validation ensures that untrusted data is examined before use, blocking the root cause of many injection and malformed-data weaknesses.

blocks

Security-by-design principles explicitly call for data validation and sanitization at every layer, reducing the chance that malformed or malicious input will be processed without scrutiny.

prevents

Requiring language-specific secure coding standards, peer review, SAST and documented mitigation of common programming errors forces validation of all inputs before they are trusted.

finds

Testing against a defined set of requirements and using code review plus vulnerability scanning forces validation of inputs and handling of unanticipated conditions, reducing the chance that malformed data will be accepted.

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-20, a class-level weakness, and none of its children carries one either.

References