CyberSecBulletin
CVE-2025-20333Exploited in the wildNVD status: Analyzed

Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow

Published Updated By the CyberSecBulletin desk

CVE-2025-20333 is a critical-severity buffer copy without checking size of input vulnerability in Cisco Secure Firewall 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 Secure Firewall Adaptive Security Appliance (ASA) Software versions: 9.8.1; 9.8.1.5; 9.8.1.7, 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 September 25, 2025, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Update Adaptive Security Appliance Software to 9.12.4.72 or 9.14.4.28 or 9.16.4.85 or 9.17.1.45, whichever matches your release line, or a later version.
  2. Update Secure Firewall Threat Defense to 7.0.8.1 or 7.2.9 or 7.4.2.4, whichever matches your release line, or a later version.
  3. CISA's required action: The KEV due date refers to the deadline by which FCEB agencies are expected to review and begin implementing the guidance outlined in Emergency Directive (ED) 25-03 (URL listed below in Notes). Agencies must follow the mitigation steps provided by CISA (URL listed below in Notes) and vendor’s instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services or discontinue use of the product if mitigations are not available.
  4. Read the advisory on sec.cloudapps.cisco.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
CiscoCisco Secure Firewall Adaptive Security Appliance (ASA) Software9.8.1; 9.8.1.5; 9.8.1.7; 9.8.2; 9.8.2.8; 9.8.2.14; 9.8.2.15; 9.8.2.17; and 32 more rangesNot stated
CiscoCisco Secure Firewall Threat Defense (FTD) Software6.2.3; 6.2.3.1; 6.2.3.2; 6.2.3.3; 6.2.3.4; 6.2.3.5; 6.2.3.6; 6.2.3.7; and 32 more rangesNot stated
CiscoAdaptive Security Appliance Software9.12 up to, but not including, 9.12.4.72; 9.14 up to, but not including, 9.14.4.28; 9.16 up to, but not including, 9.16.4.85; 9.17.0 up to, but not including, 9.17.1.45; 9.18 up to, but not including, 9.18.4.47; 9.19 up to, but not including, 9.19.1.37; 9.20 up to, but not including, 9.20.3.7; 9.22 up to, but not including, 9.22.1.39.12.4.72, 9.14.4.28, 9.16.4.85, 9.17.1.45, 9.18.4.47, 9.19.1.37
CiscoSecure Firewall Threat Defense7.0.0 up to, but not including, 7.0.8.1; 7.1.0 up to, but not including, 7.2.9; 7.3.0 up to, but not including, 7.4.2.4; 7.6.07.0.8.1, 7.2.9, 7.4.2.4

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 VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Buffer Copy without Checking Size of Input

The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output 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 Copy without Checking Size of Input vulnerabilities (CWE-120)

Timeline

  1. CVE record published.
  2. Added to CISA's Known Exploited Vulnerabilities catalogue.
  3. CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
  4. Deadline for US federal agencies to remediate, set by CISA.
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Other vulnerabilities in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software

All Cisco Secure Firewall Adaptive Security Appliance (ASA) Software vulnerabilities

Recent Buffer Copy without Checking Size of Input vulnerabilities

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