Threats / Citrix / CVE-2025-6543
CVE-2025-6543
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Citrix NetScaler ADC and Gateway vulnerability
Citrix NetScaler ADC and Gateway contain a buffer overflow vulnerability that can lead to denial of service and unintended control flow when configured as a Gateway or AAA virtual server.
Verdict
Today item — known-exploited.
A buffer overflow in NetScaler Gateway and AAA configurations enables remote denial of service and potential code execution. Active exploitation in the wild requires immediate patching for affected deployments.
CISA KEV Yes · 2025-06-305EPSS 0.10094 (verify live)6CVSS 9.23CISA SSVC Exploitation: active · Automatable: no · Impact: total4
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 2025-06-30).
Probability (EPSS)
EPSS 0.10094 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.2 (CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L) · Affected: Citrix, NetScaler ADC and Gateway. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 4.0, 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: no · Technical Impact: totalCISA'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 5 days after 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.
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 input that overflows a buffer in the NetScaler Gateway or AAA virtual server processing logic.
Business
Service availability is disrupted as the NetScaler crashes or enters an unstable state, blocking legitimate user access to corporate resources.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the buffer overflow to corrupt memory and redirect program execution to arbitrary code, gaining control over the NetScaler appliance.
Business
The attacker gains a foothold in the network perimeter, potentially enabling lateral movement, data exfiltration, or further infrastructure compromise.
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