CVE-2021-35247SolarWinds Serv-U Improper Input Validation Vulnerability
CVE-2021-35247 is a improper input validation in SolarWinds Serv-U, rated medium (5.3 on CVSS 3.1).
Why this priority: Exploited in the wild: listed in CISA's KEV catalog.
Published · Updated · NVD status: Analyzed
What it is
The software trusts input it should check, so crafted values reach code that assumes they are well formed.
How it is reached
An attacker can exploit it over the network, without an account, and nobody has to click anything.
What an attacker gains
The direct impact is limited: partial access to data or a partial outage. In practice, this kind of flaw lets an attacker drive the component into behaviour its authors did not intend.
Is it being exploited?
CISA added it to the Known Exploited Vulnerabilities catalog on 2022-01-21: it is being exploited in the wild. EPSS estimates a 3.6% chance of exploitation activity in the next 30 days, higher than 90% of scored CVEs.
What to do
- Treat it as urgent: it is on CISA's KEV list. CISA's deadline for US federal agencies: 2022-02-04.
- Upgrade SolarWinds Serv-U to 15.3 or later. The patch notes are linked below.
- Until it is patched, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
- Check exposed instances for signs of compromise, not only for the version.
Description from NVD
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.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Interfaces that accept external input. The flaw sits at the input boundary of the affected component.
Trust boundaries in play
- Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
- At the input boundary of the affected component. An attacker who crosses it can drive the component into behaviour its authors did not intend.
Questions to answer about your own systems
- Where does SolarWinds Serv-U run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.