Cisco Secure Firewall Adaptive Security…: Incorrect Calculation of Buffer Size
CVE-2026-20049 is a high-severity incorrect calculation of buffer size vulnerability in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software from Cisco, with a CVSS 3.1 base score of 7.7 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 Secure Firewall Adaptive Security Appliance (ASA) Software versions: 9.12.4.7; 9.12.4.10; 9.12.4.13, 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 0.34% 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
- Update Adaptive Security Appliance Software to 9.18.4.66 or 9.20.3.20 or 9.22.2.4 or 9.23.1.3, whichever matches your release line, or a later version.
- Update Secure Firewall Threat Defense to 7.2.11 or 7.4.3 or 7.6.4 or 7.7.10, whichever matches your release line, or a later version.
- 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 Secure Firewall Adaptive Security Appliance (ASA) Software | 9.12.4.7; 9.12.4.10; 9.12.4.13; 9.12.4.8; 9.12.4.18; 9.12.4.24; 9.12.4.26; 9.12.4.29; and 32 more ranges | Not stated |
| Cisco | Cisco Secure Firewall Threat Defense (FTD) Software | 6.4.0.10; 6.4.0.11; 6.4.0.12; 6.4.0.13; 6.4.0.14; 6.4.0.15; 6.4.0.16; 6.4.0.17; and 32 more ranges | Not stated |
| Cisco | Adaptive Security Appliance Software | 9.18.1 up to, but not including, 9.18.4.66; 9.19.1 up to, but not including, 9.20.3.20; 9.22.1.1 up to, but not including, 9.22.2.4; 9.23.1 up to, but not including, 9.23.1.3 | 9.18.4.66, 9.20.3.20, 9.22.2.4, 9.23.1.3 |
| Cisco | Secure Firewall Threat Defense | 7.2.0 up to, but not including, 7.2.11; 7.3.0 up to, but not including, 7.4.3; 7.6.0 up to, but not including, 7.6.4; 7.7.0 up to, but not including, 7.7.10 | 7.2.11, 7.4.3, 7.6.4, 7.7.10 |
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
- 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:L/UI:N/S:C/C:N/I:N/A:H. Scored by CNA (cisco.com).
Official description
A vulnerability in the processing of Galois/Counter Mode (GCM)-encrypted Internet Key Exchange version 2 (IKEv2) IPsec traffic of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to the allocation of an insufficiently sized block of memory. An attacker could exploit this vulnerability by sending crafted GCM-encrypted IPsec traffic to an affected device. A successful exploit could allow the attacker to cause an unexpected reload of the device, resulting in a DoS condition. To exploit this vulnerability, the attacker must have valid credentials to establish a VPN connection with the affected device.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Calculation of Buffer Size
The product does not correctly calculate the size to be used when allocating a buffer.
How developers prevent this class of flaw
- When allocating a buffer for the purpose of transforming, converting, or encoding an input, allocate enough memory to handle the largest possible encoding. For example, in a routine that converts & characters to & for HTML entity encoding, the output buffer needs to be at least 5 times as large as the input buffer.
- Understand the programming language's underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, not-a-number calculations, and how the language handles numbers that are too large or too small for its underlying representation. Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.
- Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
More Incorrect Calculation of Buffer Size vulnerabilities (CWE-131)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- 8.6 High severity
- 8.8 High severity
- 8.1 High severity
- 8.4 High severity
- 8.8 High severity
- 9.9 Critical severity
Recent Incorrect Calculation of Buffer Size vulnerabilities
- 7.8 High severity
- 8.4 High severity
- 9.8 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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