Threats / Citrix / CVE-2023-6549
CVE-2023-6549
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Citrix NetScaler ADC and Gateway vulnerability
Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability enabling denial-of-service attacks when configured as a Gateway or AAA virtual server.
Verdict
Today item — known-exploited.
A buffer overflow in Citrix NetScaler ADC and Gateway allows unauthenticated attackers to trigger denial-of-service conditions on affected deployments. The vulnerability is actively exploited in the wild.
CISA KEV Yes · 2024-01-175EPSS 0.57633 (verify live)6CVSS 8.23CISA SSVC Exploitation: active · Automatable: yes · Impact: partial4Exploit Public PoC / detection · nuclei template13
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
21 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2024-01-17).
Probability (EPSS)
EPSS 0.57633 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 8.2 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H) · Affected: Citrix, NetScaler ADC and NetScaler Gateway. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-119 Memory Buffer Bounds Error — weakness family: Memory safety.CWE — CNA-assigned (CVE.org); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: partialCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog the same day the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
Public exploit available
Public exploit tooling is catalogued for this CVE (a public proof-of-concept / detection template). Catalog entries: nuclei template. We link the catalog page(s) only — no payload or code is hosted or restated here.Link, never host — the catalog page is the source; basicsecurity.net does not redistribute payloads.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious request targeting the buffer overflow in the Gateway or AAA virtual server component.
Business
Service availability is disrupted as the NetScaler instance crashes or becomes unresponsive.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I send the crafted payload to the exposed NetScaler endpoint without authentication.
Business
VPN access, ICA Proxy, CVPN, RDP Proxy, or AAA services become unavailable to legitimate users.
3
Lateral reach — past segmentation narrative 3
Attacker
I repeat or automate the attack to maintain denial-of-service conditions.
Business
Business operations dependent on remote access or authentication services experience extended downtime and revenue loss.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05