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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 4 Feb 2022.
Serv UApplication · Solarwinds

CVE-2021-35247

MEDIUM · 5.3 CVSS v3.1 Published 2022-01-10
Fix available
A fix is available. Upgrade to 15.3 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Serv-U web login screen to LDAP authentication was allowing characters that were not sufficiently sanitized. SolarWinds has updated the input mechanism to perform additional validation and sanitization. Please Note: No downstream affect has been detected as the LDAP servers ignored improper characters. To insure proper input validation is completed in all environments. SolarWinds recommends scheduling an update to the latest version of Serv-U.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Serv-U's web login screen for LDAP authentication was not properly sanitizing input characters, allowing potentially malicious characters to pass through. SolarWinds addressed this by implementing additional input validation and sanitization in the authentication mechanism. While the LDAP servers reportedly ignored the improper characters, this still represents a flaw in input handling that could pose risks in different configurations.

MitigationUpdate Serv-U to the latest version to receive the improved input validation and sanitization for the LDAP authentication login screen.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Serv UApplication
Affected:< 15.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Serv-U installation and version
    Locate the Serv-U installation directory and check the version. In the Serv-U Admin Console, go to the 'About' section, or check the version via the service properties. Alternatively, check the Serv-U executable file properties for the version number.
    Affected if Installed version is earlier than 15.3 (e.g., 15.2.x, 15.1.x, etc.)
  2. Confirm LDAP authentication is enabled
    Access the Serv-U Admin Console and navigate to the authentication or security settings. Look for LDAP or Active Directory integration settings. Verify whether LDAP authentication is configured as an allowed login method.
    Affected if LDAP authentication is enabled and the Serv-U version is below 15.3
  3. Check the web login interface configuration
    Access the Serv-U web login page (typically via HTTPS on port 443 or 8080). Inspect whether the login form accepts user credentials that would be passed to an LDAP directory. In the Admin Console, verify that web-based login is enabled alongside LDAP authentication.
    Affected if Web login interface is active and LDAP authentication method is in use with a vulnerable Serv-U version

You are affected if Serv-U version is below 15.3 AND LDAP authentication is enabled for the web login screen.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 15.3 or later
Fixed in 15.3
Interim mitigation

Update Serv-U to the latest version to receive the improved input validation and sanitization for the LDAP authentication login screen.

Recommended fix Moderate confidence

Serv-U 15.3 or later (latest available version)

  1. 1. Back up your current Serv-U configuration and any custom settings
  2. 2. Download the latest version of Serv-U from the official SolarWinds download portal (documentation.solarwinds.com)
  3. 3. Review the release notes for version 15.3 or later for any configuration or migration requirements
  4. 4. Stop the Serv-U service before upgrading
  5. 5. Install the new Serv-U version using the standard installation process
  6. 6. Verify that LDAP authentication settings are intact after upgrade
  7. 7. Test the web login screen with LDAP authentication to confirm proper input validation is functioning
  8. 8. Monitor logs to ensure no validation errors occur during authentication
Caveat Standard upgrade considerations apply - review release notes for any breaking changes between your current version and 15.3+

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Serv U Exploited in the wild — priority engagement
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-35247 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data