What is CVE-2021-35211?

CVE-2021-35211 is a critical-severity vulnerability in Solarwinds Serv-U, classified under Out-of-bounds Write. CVSS score: 9.0/10. Published 2021-07-14.

How severe is CVE-2021-35211?

Critical severity. CVSS v3 base score is 9.0 out of 10.

Is CVE-2021-35211 known to be exploited?

Yes. CVE-2021-35211 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 16 public proof-of-concept repositories are indexed.

Buffer overflow in Solarwinds Serv-U

CVE-2021-35211

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.

Vulnerability class: Buffer Overflow

Published 2021-07-14 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.912 (99.8th percentile), scored 2026-10-19.

High probability of exploitation in the next 30 days — patch promptly. 100th percentile — 99.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.912 · newest: 0.912 · change: 0.000

Affected products

Solarwinds Serv-U — versions 15.2.3
Solarwinds Serv-U Managed File Transfer Server And Secured FTP — versions SolarWinds Serv-U

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2021-11-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2021-11-17.

Required action: Apply updates per vendor instructions.

Known ransomware campaign use: yes.

Public proof-of-concept exploits

References

www.solarwinds.com/trust-center/security-advisories/cve-2021-35211 (Patch, Vendor Advisory)
www.microsoft.com/security/blog/2021/07/13/microsoft-discovers-threat-actor-tar… (Patch, Vendor Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-35211?: CVE-2021-35211 is a critical-severity vulnerability in Solarwinds Serv-U, classified under Out-of-bounds Write. CVSS score: 9.0/10. Published 2021-07-14.
How severe is CVE-2021-35211?: Critical severity. CVSS v3 base score is 9.0 out of 10.
Is CVE-2021-35211 known to be exploited?: Yes. CVE-2021-35211 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating it is being actively exploited. 16 public proof-of-concept repositories are indexed.