CVE Intelligence
CISA KEV High Memory corruption

CVE-2023-6549 — Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

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

Published Jan 17, 2024 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, CVE Program (cve.org) e CISA ADP, NIST National Vulnerability Database, GitHub Security Advisories · CNA: Citrix

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Jan 17, 2024 Detection templates (Nuclei) · 1
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • Public exploit/PoC (nuclei)+4
  • EPSS 57.6% (30-day exploitation probability)+15
  • Technical severity (high)+6
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Jan 17, 2024
EPSS FIRST
57.63%
ahead of 99% of scored CVEs · Oct 14, 2026
Affects
Citrix
Netscaler Application Delivery Controller and 2 more
CVSS base
7.5
High · 4 source(s)
Prioritization reference: 8.2 provisional

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

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

US federal deadline: Feb 7, 2024 — passed 981 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Citrix Netscaler Application Delivery Controller, Citrix Netscaler Gateway, Cloud Software Group NetScaler ADC).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  4. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  5. EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
  6. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Citrix Netscaler Application Delivery Controller ≥ 12.1 and < 12.1-55.302≥ 13.0 and < 13.0-92.21≥ 13.1 and < 13.1-37.176≥ 13.1 and < 13.1-51.15≥ 14.1 and < 14.1-12.35 Vulnerable NIST National Vulnerability Database
Citrix Netscaler Gateway ≥ 13.0 and < 13.0-92.21≥ 13.1 and < 13.1-51.15≥ 14.1 and < 14.1-12.35 Vulnerable NIST National Vulnerability Database
Cloud Software Group NetScaler ADC ≥ 14.1 and < 12.35≥ 13.1 and < 51.15≥ 13.0 and < 92.21≥ 13.1-FIPS and < 37.176≥ 12.1-FIPS and < 55.302≥ 12.1-NDcPP and < 55.302 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
8.2 CVSS 3.1 High 3.9 4.2 secure@citrix.com via NIST National Vulnerability Database
8.2 CVSS 3.1 High — — GitHub, Inc. via GitHub Security Advisories
8.2 CVSS 3.1 High — — Citrix via CVE Program (cve.org) e CISA ADP
7.5 CVSS 3.1 High 3.9 3.6 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)
Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 8.2 (secure@citrix.com via NIST National Vulnerability Database) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-119 · Buffer Errors (Improper Restriction of Operations within Memory Bounds)

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Jan 17, 2024
Federal deadline
Feb 7, 2024
passed 981 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Detection templates (Nuclei)

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 57.63%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
  • Hunt retroactively in logs from before Jan 17, 2024 (KEV listing): exploitation may have started earlier.
web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · citrix/netscaler application delivery controller, citrix/netscaler gateway
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 8.2 → 7.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · Published → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record published
    Oct 13, 2026
  • Affected products added · cloud software group/netscaler adc
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • CVSS changed · 8.2
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · → Published
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2024
  • CVE published
    Jan 17, 2024 · Citrix
  • Added to CISA KEV catalog
    Jan 16, 2024 · CISA

Source activity

Repeated readings are counted rather than listed.

  • 3× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

Elsewhere on this site

Citrix
every CVE for this vendor
2024-01
what else CISA listed that month
Memory corruption
same class
CWE-119
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-88779 Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer Vulnerability KEV 11d
  • CVE-2026-88778 Predictable exact value from previous values vulnerability in Citrix NetScaler ADC and… 18d
  • CVE-2026-88777 Buffer Errors (Improper Restriction of Operations within Memory Bounds) in Citrix Netscaler Application Delivery Controller 18d
  • CVE-2026-88774 Improper Input Validation in Citrix Netscaler Application Delivery Controller 18d
  • CVE-2026-88776 Buffer Errors (Improper Restriction of Operations within Memory Bounds) in Citrix Netscaler Application Delivery Controller 18d
  • CVE-2026-88775 Classic Buffer Overflow in Citrix Netscaler Application Delivery Controller 18d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2023-6549 is "Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability", rated High. It affects Netscaler Application Delivery Controller (Citrix); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 7.5 describes technical severity. EPSS 57.63% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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