Serv-U: Improper Encoding or Escaping of Output
CVE-2025-40547 is a critical-severity improper encoding or escaping of output vulnerability in Serv-U from SolarWinds, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an attacker with administrator privileges, without any action from a user. Affected Serv-U versions: SolarWinds Serv-U 15.5.2 and prior versions. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.97% chance of exploitation within 30 days, higher than 62% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of Serv-U you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on solarwinds.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| SolarWinds | Serv-U | SolarWinds Serv-U 15.5.2 and prior versions | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- HighAdministrator-level access is required first.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (solarwinds.com).
Official description
A logic error vulnerability exists in Serv-U which when abused could give a malicious actor with access to admin privileges the ability to execute code. This issue requires administrative privileges to abuse. On Windows deployments, the risk is scored as a medium because services frequently run under less-privileged service accounts by default.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Encoding or Escaping of Output
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
How developers prevent this class of flaw
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
- If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
- Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
More Improper Encoding or Escaping of Output vulnerabilities (CWE-116)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other vulnerabilities in Serv-U
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
Recent Improper Encoding or Escaping of Output vulnerabilities
- 8.6 High severity
- 8.1 High severity
- 9.4 Critical severity
- 10.0 Critical severity
- 10.0 Critical severity
- 7.5 High severity
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