VulnerabilityPublished 17 Jan 2024Updated 21 Oct 2025

CVE-2023-6549: Cloud Software Group NetScaler ADC · Memory Buffer Overflow

Affects Cloud Software Group NetScaler ADCSource CVE Database V5

Exploited in the wild · KEV due 7 Feb 2024 · public detection template (Nuclei) · 57% EPSS : apply the vendor's fix or mitigations to Cloud Software Group NetScaler ADC now.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

8.2High

How severe the flaw is on the 0–10 CVSS scale.

KEV deadline: 7 Feb 2024 US federal agencies must patch by this date; a sensible deadline for everyone else.
EPSS: 57.6% chance of exploitation in 30 days – higher than 99% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 17 Jan 2024
Detectable: evidence found.
nuclei template: Citrix Netscaler ADC & Gateway - Out-Of-Bounds Memory Read
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: evidence found.
Listed in CISA KEV the same day as disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by Citrix Systems, Inc.
6 Dec 202311:01 UTC, 42 days before disclosure
CVE published
on cve.org
17 Jan 202420:15 UTC, t = 0
Added to CISA KEV (opens in a new tab)
exploitation confirmed
17 Jan 2024, the same day as disclosure
KEV remediation due
US federal deadline
7 Feb 2024, 21 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Affected software

Product	Affected	Fixed in
Cloud Software Group NetScaler ADC	Affected 12.1-FIPS – 14.1 6 affected builds	Fixed in–

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

Impact

For European organizations, this vulnerability poses a significant risk to the availability and integrity of network infrastructure services. NetScaler ADC and Gateway are widely used for load balancing, secure remote access, and application delivery, often in enterprise, government, and critical infrastructure environments. Exploitation could lead to denial of service, disrupting business operations, remote access capabilities, and potentially exposing sensitive memory contents through out-of-bounds reads. This could affect sectors such as finance, healthcare, telecommunications, and public administration, where service continuity and data integrity are paramount. The unauthenticated nature of the exploit increases the threat surface, allowing attackers to target exposed NetScaler devices directly from the internet. Disruptions could lead to operational downtime, loss of productivity, and reputational damage. Additionally, memory disclosure could aid attackers in further exploitation or reconnaissance activities.

Mitigation

1. Immediately inventory all NetScaler ADC and Gateway devices to identify affected versions (12.1-FIPS, 12.1-NDcPP, 13.0, 13.1, 13.1-FIPS, 14.1). 2. Monitor Cloud Software Group (Citrix) advisories closely for official patches or hotfixes and apply them as soon as they become available. 3. Restrict external network access to NetScaler management interfaces and gateways using firewalls, VPNs, or access control lists to limit exposure. 4. Implement network-level anomaly detection to identify unusual traffic patterns or repeated connection attempts targeting NetScaler devices. 5. Employ rate limiting and intrusion prevention systems (IPS) to mitigate potential exploitation attempts. 6. Conduct regular security assessments and penetration tests focusing on network infrastructure components. 7. Consider temporary compensating controls such as disabling vulnerable features or services if patching is delayed. 8. Maintain up-to-date backups and incident response plans to quickly recover from potential denial of service incidents.

CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer (opens in a new tab)
Class weaknessLikelihood of exploit: High
The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Operation · Build and Compilation · Environment Hardening
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…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Buffer Overflow via Environment Variables (opens in a new tab)
Overflow Buffers (opens in a new tab)
Client-side Injection-induced Buffer Overflow (opens in a new tab)
Filter Failure through Buffer Overflow (opens in a new tab)
MIME Conversion (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 21 Oct 2025, 19:59 UTC

Public exploits and detectiona Nuclei detection template

WeaknessesCWE-119

Technical details

References

Community reviews

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