A vulnerability in the Remote Access VPN feature of Cisco Adaptive Security Appliance (ASA)…
CVE-2024-20495 is a high-severity improper input validation vulnerability in Cisco Adaptive Security Appliance (ASA) Software from Cisco, with a CVSS 3.1 base score of 8.6 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Cisco Adaptive Security Appliance (ASA) Software versions: 9.8.4.12; 9.8.4.15; 9.8.4.17, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.52% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Cisco Adaptive Security Appliance (ASA) Software you run against the affected versions below, and install the vendor's latest release.
- 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 Adaptive Security Appliance (ASA) Software | 9.8.4.12; 9.8.4.15; 9.8.4.17; 9.8.4.25; 9.8.4.20; 9.8.4.22; 9.8.4.26; 9.8.4.29; and 32 more ranges | Not stated |
| Cisco | Cisco Firepower Threat Defense Software | 6.2.3.16; 6.2.3.17; 6.2.3.18; 6.6.0; 6.6.0.1; 6.6.1; 6.6.3; 6.6.4; and 32 more ranges | Not stated |
| Cisco | adaptive_security_appliance_software | 9.8.4.12; 9.8.4.15; 9.8.4.17; 9.8.4.25; 9.8.4.20; 9.8.4.22; 9.8.4.26; 9.8.4.29; and 32 more ranges | Not stated |
| Cisco | firepower_threat_defense_software | 6.2.3.16; 6.2.3.17; 6.2.3.18; 6.6.0; 6.6.0.1; 6.6.1; 6.6.3; 6.6.4; and 32 more ranges | Not stated |
| Cisco | Secure Firewall Threat Defense | 6.2.3.16; 6.2.3.17; 6.2.3.18; 6.4.0.8; 6.4.0.9; 6.4.0.10; 6.4.0.11; 6.4.0.12; and 32 more ranges | 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
- 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
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H. Scored by CNA (cisco.com).
Official description
A vulnerability in the Remote Access VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition on an affected device. This vulnerability is due to improper validation of client key data after the TLS session is established. An attacker could exploit this vulnerability by sending a crafted key value to an affected system over the secure TLS session. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
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.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in Cisco Adaptive Security Appliance (ASA) Software
- 9.0 Critical severity
- 8.6 High severity
- 8.6 High severity
- 8.5 High severity
- 7.7 High severity
- 8.6 High severity
Recent Improper Input Validation vulnerabilities
- 9.2 Critical severity
- 9.8 Critical severity
- 8.1 High severity
- 8.1 High severity
- 8.5 High severity
- 9.1 Critical severity
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