External risk intelligence

SolarWinds Serv-U Web Authentication Input Validation Flaw

CVE advisoryKnown Exploit

CVE-2021-35247

Serv-U's web login screen accepted unsanitized characters, creating a risk of unauthorized data modification. While downstream systems mitigated the impact, organizations using affected versions should update to ensure proper input validation.

5Halo Surface Signal

Solarwinds Serv U

before 15.3

External exposure likelihood

Halo Surface Signal score for CVE-2021-35247

This vulnerability affects the web login interface of the Serv-U file transfer software. As an internet-facing service designed for remote file management and transfer, the web login portal is typically exposed to the public internet by design to facilitate authorized remote access.

CVSS vector

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

Horizon Alert

Summary of the vulnerability and why it matters

The Serv-U web login screen has a vulnerability related to how it handles data. The system did not adequately clean certain characters in the input, which could potentially allow for unauthorized modifications. Although downstream systems ignored the improper characters, it is recommended to update Serv-U to ensure proper input validation.

  • Vulnerable: Serv-U web login screen
  • Flaw: Insufficient input sanitization
  • Impact: Unauthorized data modification

Attack Path

How an attacker could exploit the issue

The Serv-U web login screen accepted unsanitized characters, allowing attackers to construct malicious queries. While downstream LDAP servers ignored these characters, the input validation mechanism could be exploited. Organizations using affected Serv-U versions are advised to update to the latest version to ensure proper input validation.

  • Serv-U web login exposed externally.
  • Attacker sends un-sanitized input.
  • Input control leads to data impact.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in Serv-U software could allow unauthorized individuals to attempt to bypass authentication. While downstream impacts were not detected due to LDAP server handling of improper characters, organizations are advised to implement updates to ensure robust input validation and security. The potential for unauthorized access, even if mitigated by other systems, represents a business risk.

  • Attackers likely need moderate skill.
  • Requires public internet access.
  • Business risk is medium urgency.

Priority actions

Operational Fix

Recommended remediation, mitigation, and detection steps

The Serv-U web login screen exhibited an improper input validation vulnerability that allowed unsanitized characters in queries. While downstream effects were not detected as LDAP servers ignored these characters, SolarWinds recommends updating to the latest Serv-U version to ensure proper input validation. This issue poses a potential risk to organizations utilizing affected Serv-U versions.

  • Identify Serv-U assets with versions prior to 15.3.
  • Isolate affected systems if immediate patching is not possible.
  • Apply the vendor update, verify the fix, and monitor for related activity.

Frequently asked questions

What is SolarWinds Serv-U used for?

SolarWinds Serv-U is a file transfer solution that includes a web login screen. People use it to manage and transfer files remotely, often enabling access over the internet.

What is the weakness in CVE-2021-35247?

CVE-2021-35247 is an improper input validation vulnerability. The Serv-U web login screen did not properly clean or sanitize certain characters entered by users, which is a weakness classified as CWE-20.

How can this Serv-U vulnerability be triggered?

An attacker could trigger this vulnerability by constructing and sending specific queries with unsanitized characters to the Serv-U web login screen. The vulnerability is not triggered if the input is properly sanitized before processing.

Who needs to care about CVE-2021-35247?

Organizations running SolarWinds Serv-U, especially versions prior to 15.3, should care. This is because the web login interface is typically internet-facing, increasing the potential for external access to this vulnerability. [cite:HALO]

What is the first step to address this Serv-U vulnerability?

The first step is to identify all Serv-U assets and check their versions, specifically looking for those earlier than 15.3. If immediate patching isn't possible, consider isolating affected systems while preparing to apply the vendor update.

References

Sources and related resources

Primary sources: NVD, CVE.org, CISA KEV.

NVDPublished Modified