Cisco NX-OS Software: Buffer Access with Incorrect Length Value
CVE-2025-20191 is a high-severity buffer access with incorrect length value vulnerability in Cisco NX-OS Software from Cisco, with a CVSS 3.1 base score of 7.4 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected Cisco NX-OS Software versions: 8.2(5); 7.3(5)D1(1); 8.4(2), 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 0.24% 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 NX-OS Software you run against the affected versions below, and install the vendor's latest release.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Cisco | Cisco NX-OS Software | 8.2(5); 7.3(5)D1(1); 8.4(2); 8.4(3); 9.2(3); 9.2(2v); 7.3(4)D1(1); 8.2(1); and 32 more ranges | Not stated |
| Cisco | Cisco Wireless LAN Controller (WLC) | 8.10.112.0; 8.8.120.0; 8.3.143.0; 8.3.111.0; 8.2.164.0; 8.5.109.0; 8.3.132.0; 8.5.105.0; 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
- AdjacentThe attacker must be on the same local network segment.
- 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:A/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 Switch Integrated Security Features (SISF) of Cisco IOS Software, Cisco IOS XE Software, Cisco NX-OS Software, and Cisco Wireless LAN Controller (WLC) AireOS Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to the incorrect handling of DHCPv6 packets. An attacker could exploit this vulnerability by sending a crafted DHCPv6 packet to an affected device. 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: Buffer Access with Incorrect Length Value
The product uses a sequential operation to read or write a buffer, but it uses an incorrect length value that causes it to access memory that is outside of the bounds of the buffer.
How developers prevent this class of flaw
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.
More Buffer Access with Incorrect Length Value vulnerabilities (CWE-805)
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 references
Other vulnerabilities in Cisco NX-OS Software
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
Recent Buffer Access with Incorrect Length Value vulnerabilities
- 7.4 High severity
- 7.5 High severity
- 7.4 High severity
- 7.7 High severity
- 7.7 High severity
- 7.7 High severity
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