Cisco Multiple Products Improper Input Validation
CVE-2025-20393 is a critical-severity improper input validation vulnerability in Cisco Secure Email from Cisco, with a CVSS 3.1 base score of 10.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Cisco Secure Email versions: 14.0.0-698; 13.5.1-277; 13.0.0-392, and others listed below. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on December 17, 2025, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Asyncos to 15.0.5-016 or 15.5.4-012 or 16.0.4-016 or 15.0.2-007, whichever matches your release line, or a later version.
- CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- Read the advisory on sec.cloudapps.cisco.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cisco | Cisco Secure Email | 14.0.0-698; 13.5.1-277; 13.0.0-392; 14.2.0-620; 13.0.5-007; 13.5.4-038; 14.2.1-020; 14.3.0-032; and 10 more ranges | Not stated |
| Cisco | Cisco Secure Email and Web Manager | 13.6.2-023; 13.6.2-078; 13.0.0-249; 13.0.0-277; 13.8.1-052; 13.8.1-068; 13.8.1-074; 14.0.0-404; and 18 more ranges | Not stated |
| Cisco | Asyncos | before 15.0.5-016; 15.5 up to, but not including, 15.5.4-012; 16.0 up to, but not including, 16.0.4-016; before 15.0.2-007; 15.5 up to, but not including, 15.5.4-007; 16.0 up to, but not including, 16.0.4-010 | 15.0.5-016, 15.5.4-012, 16.0.4-016, 15.0.2-007, 15.5.4-007, 16.0.4-010 |
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
- NoneNo account or login is needed.
- 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:N/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (cisco.com).
Official description
A vulnerability in the Spam Quarantine feature of Cisco AsyncOS Software for Cisco Secure Email Gateway and Cisco Secure Email and Web Manager could allow an unauthenticated, remote attacker to execute arbitrary system commands on an affected device with root privileges. This vulnerability is due to insufficient validation of HTTP requests by the Spam Quarantine feature. An attacker could exploit this vulnerability by sending a crafted HTTP request to the affected device. A successful exploit could allow the attacker to execute arbitrary commands on the underlying operating system with root privileges.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How developers prevent this class of flaw
- Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
- Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20393US Government Resource
Other vulnerabilities in Cisco Secure Email
- 9.8 Critical severity
- 9.8 Critical severity
Cisco Secure Email Gateway SQL Injection Exploited
- 9.8 Critical severity
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
Recent Improper Input Validation vulnerabilities
- 9.0 Critical severity
- 7.2 High severity
- 7.2 High severity
- 9.8 Critical severity
- 7.5 High severity
- 7.8 High severity
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