CVE-2021-35247 — SolarWinds Serv-U Improper Input Validation Vulnerability

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: Feb 4, 2022 — passed 1714 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Solarwinds Serv-u).
2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
3. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
4. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
5. Search available logs for exploit probes matching the vulnerability class (input validation), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-20 · Improper Input Validation

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 3.45%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
• Hunt retroactively in logs from before Jan 21, 2022 (KEV listing): exploitation may have started earlier.

Timeline

What happened to this CVE, newest first.

• 2026
• Affected products added · solarwinds/serv-u
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• Affected products added · solarwinds/serv-u
  Oct 13, 2026 · NIST National Vulnerability Database
• CVSS changed · 5.3
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Analyzed
  Oct 13, 2026 · NIST National Vulnerability Database
• Added to CISA KEV (detected)
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• Record created in this database
  Oct 13, 2026 · CISA Known Exploited Vulnerabilities
• 2022
• Added to CISA KEV catalog
  Jan 20, 2022 · CISA
• CVE published
  Jan 10, 2022 · SolarWinds

Source activity

Repeated readings are counted rather than listed.

• 2× References added · Oct 13, 2026 – Oct 13, 2026
• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

5 on the record

• documentation.solarwinds.com/en/success_center/servu/content/release_notes/servu_15-3_release_note
  Release Notes, Vendor Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.solarwinds.com/trust-center/security-advisories/cve-2021-35247
  Broken Link, Vendor Advisory, x_refsource_MISC, NIST National Vulnerability Database
• www.cisa.gov/known-exploited-vulnerabilities-catalog
  US Government Resource, NIST National Vulnerability Database
• github.com/advisories/GHSA-jqwj-9jvg-583v
  GitHub Security Advisories
• nvd.nist.gov/vuln/detail/CVE-2021-35247
  GitHub Security Advisories

Elsewhere on this site

Related CVEs (same products)

• Critical CVE-2026-28321 SolarWinds Serv-U Broken Access Control Vulnerability Jul 21, 2026
• Critical CVE-2026-28317 SolarWinds Serv-U Insecure Direct Object Reference (IDOR) Vulnerability Jul 21, 2026
• Critical CVE-2026-28313 SolarWinds Serv-U Insecure Direct Object Reference (IDOR) Vulnerability Jul 21, 2026
• Critical CVE-2026-28312 SolarWinds Serv-U Privilege Escalation Vulnerability Jul 21, 2026
• Critical CVE-2026-28314 SolarWinds Serv-U Insecure Direct Object Reference (IDOR) Vulnerability Jul 21, 2026
• Critical CVE-2026-28316 SolarWinds Serv-U Insecure Direct Object Reference (IDOR) Vulnerability Jul 21, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No fixed version, patch or mitigation documented.
• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-35247 is "SolarWinds Serv-U Improper Input Validation Vulnerability", rated Medium. It affects Serv-u (Solarwinds); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 5.3 describes technical severity. EPSS 3.45% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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