Security readout for executives and security teams
Plain-English summary
SolarWinds Serv-U 15.2.5 and earlier had insufficient input validation on the web login path when LDAP authentication was used. SolarWinds says LDAP servers ignored the improper characters and no downstream effect was detected, but CISA lists the CVE as known exploited, so exposed deployments should not treat the medium CVSS score as low urgency.
Executive priority
Treat this as a priority remediation item despite the medium CVSS score because it is in CISA KEV. The business action is straightforward: find Serv-U, determine whether affected versions remain, and update on an accelerated schedule.
Technical view
CVE-2021-35247 is a CWE-20 improper input validation issue in Serv-U web login handling for LDAP authentication. The CVSS 3.1 score is 4.3 with network attack vector, low complexity, no privileges, user interaction required, and low integrity impact. SolarWinds addressed it with additional validation and sanitization and recommends updating to the latest Serv-U version.
Likely exposure
Exposure is limited to SolarWinds Serv-U 15.2.5 and previous versions, specifically environments using the web login screen with LDAP authentication. Internet-accessible login portals increase operational concern, but the source bundle does not identify specific vulnerable configurations beyond Serv-U version and LDAP login path.
Exploitation context
CISA KEV status supports known exploitation. The provided sources do not describe exploitation details, payloads, attacker groups, indicators of compromise, or downstream impact. SolarWinds states no downstream effect was detected because LDAP servers ignored improper characters.
Researcher notes
The public bundle supports affected version, vulnerable component, CWE, CVSS, vendor remediation direction, and KEV status. It does not provide exploit mechanics, proof-of-concept details, IOCs, or confirmed business impact. Avoid extrapolating beyond input validation in Serv-U LDAP web login handling.
Mitigation direction
- Update Serv-U to the latest vendor-supported version per SolarWinds guidance.
- Prioritize remediation for internet-facing or LDAP-enabled Serv-U deployments.
- Review SolarWinds Serv-U 15.3 release notes for upgrade planning.
- Check CISA KEV guidance for required remediation timelines.
- Monitor vendor advisory updates for additional mitigations or indicators.
Validation and detection
- Inventory all Serv-U instances and record exact product versions.
- Identify whether web login with LDAP authentication is enabled.
- Confirm no instance remains on Serv-U 15.2.5 or earlier.
- Verify upgraded systems use the updated validation and sanitization release.
- Review access logs for unusual login behavior, without assuming compromise from this CVE alone.
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-20: 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 lookupCVE-2021-35247 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
- Medium
- CVSS
- 4.3 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
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:L/PR:N/UI:R/S:U/C:N/I:L/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://www.solarwinds.com/trust-center/security-advisories/cve-2021-35247CVE reference · x_refsource_MISC
- https://documentation.solarwinds.com/en/success_center/servu/content/release_notes/servu_15-3_release_notes.htmCVE reference · x_refsource_MISC
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-35247CVE 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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.