Security readout for executives and security teams
Plain-English summary
CVE-2021-35211 is a critical SolarWinds Serv-U flaw that can let a remote attacker execute code and gain privileged access on the server hosting Serv-U. It affects Serv-U Managed File Transfer and Secure FTP for Windows before 15.2.3 HF2.
Executive priority
Treat as urgent for any organization running Serv-U on Windows. KEV status means exploitation has been observed, and the potential impact is full compromise of the Serv-U host.
Technical view
The vulnerability is described as a Remote Memory Escape issue in SolarWinds Serv-U, mapped to CWE-787. CVSS 3.1 is 9.0 with network attack vector, no required privileges or user interaction, high attack complexity, changed scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most likely where SolarWinds Serv-U Managed File Transfer or Secure FTP for Windows is deployed below version 15.2.3 HF2, especially if reachable from untrusted networks.
Exploitation context
Active exploitation is supported by CISA KEV listing and Microsoft’s report of a threat actor targeting SolarWinds Serv-U with a zero-day exploit. The provided sources do not establish broad commodity exploitation details.
Researcher notes
Evidence supports critical severity, affected Windows Serv-U versions before 15.2.3 HF2, and active exploitation. The bundle does not provide safe exploit indicators, detailed vulnerable code paths, or complete detection logic, so validation should remain version, exposure, and forensic-review based.
Mitigation direction
- Identify all SolarWinds Serv-U Managed File Transfer and Secure FTP Windows servers.
- Upgrade affected Serv-U installations to 15.2.3 HF2 or later vendor-supported guidance.
- Review SolarWinds advisory for any product-specific hardening or detection advice.
- Restrict Serv-U exposure to trusted networks where business requirements allow.
- Investigate affected servers for compromise indicators from Microsoft and SolarWinds guidance.
Validation and detection
- Confirm installed Serv-U product and version on each Windows server.
- Verify no Serv-U installation remains below 15.2.3 HF2.
- Check whether Serv-U services are internet-facing or exposed to untrusted networks.
- Review Serv-U and host logs around the exploitation disclosure period.
- Confirm vulnerability status against CISA KEV and vendor advisory records.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-787: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-35211 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H2.26Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9CriticalVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35211CVE reference · x_refsource_MISC
- https://www.microsoft.com/security/blog/2021/07/13/microsoft-discovers-threat-actor-targeting-solarwinds-serv-u-software-with-0-day-exploitCVE reference · x_refsource_MISC
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-35211CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.