CVE-2021-35211: SolarWinds Serv-U Remote Code Execution Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 3 Nov 2021, 112 days after the CVE record was published.

How likely is exploitation in the next 30 days?

91.2%

EPSS score, percentile 99.8 of all scored records

How severe?

9.0 Critical

CVSS v3.1 base score, given by the CNA

What should I do?

Required action (CISA), due 17 Nov 2021: Apply updates per vendor instructions.

The CVE record links no vendor advisory, patch or mitigation.

Which versions are affected?

Affected: SolarWinds Serv-U up to, not including, 15.2.3 HF1

Versions by product

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

CISA due date for this action: 17 November 2021.

Solution (from the CVE record)

SolarWinds has released a hotfix 15.2.3 HF2 It is suggested to upgrade to the latest hotfix as soon as possible

Workaround (from the CVE record)

SolarWinds advises to disconnect Serv-U Server from internet until patched.

Advisories and patches

The CVE record links no vendor advisory, patch or mitigation.

Linked from CISA's catalog entry

• https://nvd.nist.gov/vuln/detail/CVE-2021-35211

Affected products and versions

As listed in the CVE record.

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 contains an unspecified memory escape vulnerability which can allow for remote code execution.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2021-35211 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
• CISA marks it as known to be used in ransomware campaigns.
• The due date CISA sets for the required action is 17 Nov 2021.
• The CVE record was published on 14 Jul 2021, 112 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 9.0 (Critical), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 91.2% (percentile 99.8), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

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

Serv-U Remote Memory Escape Vulnerability

Microsoft discovered a remote code execution (RCE) vulnerability in the SolarWinds Serv-U product utilizing a Remote Memory Escape Vulnerability. If exploited, a threat actor may be able to gain privileged access to the machine hosting Serv-U Only. SolarWinds Serv-U Managed File Transfer and Serv-U Secure FTP for Windows before 15.2.3 HF2 are affected by this vulnerability.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-787: Out-of-bounds Write

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

References

• solarwinds.com
• microsoft.com

More exploited SolarWinds vulnerabilities

• CVE-2026-28318: SolarWinds Serv-U Uncontrolled Resource Consumption Vulnerability (added 5 Jun 2026)
• CVE-2025-26399: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability (added 9 Mar 2026)
• CVE-2025-40536: SolarWinds Web Help Desk Security Control Bypass Vulnerability (added 12 Feb 2026)
• CVE-2025-40551: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability (added 3 Feb 2026)
• CVE-2024-28987: SolarWinds Web Help Desk Hardcoded Credential Vulnerability (added 15 Oct 2024)
• CVE-2024-28986: SolarWinds Web Help Desk Deserialization of Untrusted Data Vulnerability (added 15 Aug 2024)