Cisco Adaptive Security Appliance (ASA) Software: Improper Neutralization of Expression/Command Delimiters
CVE-2024-20329 is a critical-severity improper neutralization of expression/command delimiters vulnerability in Cisco Adaptive Security Appliance (ASA) Software from Cisco, with a CVSS 3.1 base score of 9.9 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected Cisco Adaptive Security Appliance (ASA) Software versions: 9.17.1; 9.17.1.7; 9.17.1.9, 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 1.15% chance of exploitation within 30 days, higher than 67% of scored CVEs.
Critical severity: a successful attack would have severe impact.
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.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cisco | Cisco Adaptive Security Appliance (ASA) Software | 9.17.1; 9.17.1.7; 9.17.1.9; 9.17.1.10; 9.18.1; 9.18.1.3; 9.17.1.11; 9.18.2; and 19 more ranges | Not stated |
| Cisco | adaptive_security_appliance_software | 9.17.1 through 9.17.1.33; 9.18.1; 9.18.1.3; 9.18.2 through 9.18.2.8; 9.18.3 through 9.18.3.56; 9.19.1 through 9.19.1.18 | 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
- LowA basic user account is enough.
- 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:L/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (cisco.com).
Official description
A vulnerability in the SSH subsystem of Cisco Adaptive Security Appliance (ASA) Software could allow an authenticated, remote attacker to execute operating system commands as root. This vulnerability is due to insufficient validation of user input. An attacker could exploit this vulnerability by submitting crafted input when executing remote CLI commands over SSH. A successful exploit could allow the attacker to execute commands on the underlying operating system with root-level privileges. An attacker with limited user privileges could use this vulnerability to gain complete control over the system.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Expression/Command Delimiters
The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as expression or command delimiters when they are sent to a downstream component.
How developers prevent this class of flaw
- Developers should anticipate that inter-expression and inter-command delimiters will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
- While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
- Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
More Improper Neutralization of Expression/Command Delimiters vulnerabilities (CWE-146)
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
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 Neutralization of Expression/Command Delimiters vulnerabilities
- 7.2 High severity
- 7.8 High severity
- 7.4 High severity
Spotted an error? Tell us.