Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow
CVE-2023-6549 is a high-severity improper restriction of operations within the bounds of a memory buffer vulnerability in NetScaler ADC from Cloud Software Group, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 12.35, 51.15, 92.21 as the first without the flaw, so updating NetScaler ADC to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on January 17, 2024, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update NetScaler ADC to 12.35 or 51.15 or 92.21 or 37.176, whichever matches your release line, or a later version.
- Update Netscaler Application Delivery Controller to 12.1-55.302 or 13.0-92.21 or 13.1-37.176 or 13.1-51.15, whichever matches your release line, or a later version.
- Update Netscaler Gateway to 13.0-92.21 or 13.1-51.15 or 14.1-12.35, whichever matches your release line, or a later version.
- CISA's required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- Read the advisory on support.citrix.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 |
|---|---|---|---|
| Cloud Software Group | NetScaler ADC | 14.1 up to, but not including, 12.35; 13.1 up to, but not including, 51.15; 13.0 up to, but not including, 92.21; 13.1-FIPS up to, but not including, 37.176; 12.1-FIPS up to, but not including, 55.302; 12.1-NDcPP up to, but not including, 55.302 | 12.35, 51.15, 92.21, 37.176, 55.302 |
| Citrix | Netscaler Application Delivery Controller | 12.1 up to, but not including, 12.1-55.302; 13.0 up to, but not including, 13.0-92.21; 13.1 up to, but not including, 13.1-37.176; 13.1 up to, but not including, 13.1-51.15; 14.1 up to, but not including, 14.1-12.35 | 12.1-55.302, 13.0-92.21, 13.1-37.176, 13.1-51.15, 14.1-12.35 |
| Citrix | Netscaler Gateway | 13.0 up to, but not including, 13.0-92.21; 13.1 up to, but not including, 13.1-51.15; 14.1 up to, but not including, 14.1-12.35 | 13.0-92.21, 13.1-51.15, 14.1-12.35 |
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
- UnchangedImpact stays within the vulnerable component.
- 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:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.2 | High | CNA (citrix.com) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Improper Restriction of Operations within the Bounds of a Memory Buffer in NetScaler ADC and NetScaler Gateway allows Unauthenticated Denial of Service and Out-Of-Bounds Memory Read
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Restriction of Operations within the Bounds of a Memory Buffer
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary.
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.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-6549US Government Resource
Other vulnerabilities in NetScaler ADC
- 8.8 High severity
- 7.5 High severity
Recent Improper Restriction of Operations within the Bounds of a Memory Buffer vulnerabilities
- 7.8 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
- 7.1 High severity
- 7.8 High severity
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