CVE-2025-5777 : Critical Citrix NetScaler Memory Vulnerability

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June 27, 2025
CVE-2025-5777: Critical Citrix NetScaler Memory Vulnerability

Citrix NetScaler has a critcal security flaw tracked as CVE-2025-5777. This bug lets attackers read memory they shouldn’t have access to when NetScaler runs as a Gateway or AAA server. The vulnerability has a CVSS score of 9.3, which puts it in the critical category.

The problem occurs because NetScaler doesn’t properly check input data, allowing attackers to read beyond normal memory boundaries. This means sensitive information stored in memory could be exposed to unauthorized users.

Basic Details

CVE ID: CVE-2025-5777
CVSS Score: 9.3 (Critical)
Type: Out-of-bounds memory read (CWE-125)
Reported: June 17, 2025
Updated: June 23, 2025

The Problem

NetScaler doesn’t validate input properly in certain configurations. When an attacker sends specially crafted data, the system reads memory it shouldn’t access. This can leak sensitive information like passwords, session tokens, or configuration data.

What’s Affected

This vulnerability affects NetScaler when configured as:

  • Gateway (VPN virtual server)
  • ICA Proxy
  • Clientless VPN (CVPN)
  • RDP Proxy
  • AAA virtual server

Affected Versions:

  • NetScaler ADC and Gateway 14.1 before 14.1-43.56
  • NetScaler ADC and Gateway 13.1 before 13.1-58.32
  • NetScaler ADC 13.1-FIPS/NDcPP before 13.1-37.235
  • NetScaler ADC 12.1-FIPS before 12.1-55.328
  • NetScaler ADC and Gateway 12.1 and 13.0 (End-of-Life versions)

If your NetScaler isn’t configured for these services, you’re not at risk from CVE-2025-5777.

Note: A related vulnerability, CVE-2025-5349 (CVSS 8.7), affects the Management Interface and was also patched in the same security bulletin.

Why This Matters

This vulnerability is critical for several reasons:
No authentication needed – Attackers don’t need to log in or have any credentials Network accessible – Can be exploited remotely over the internet High impact – Can expose confidential data, disrupt services, or compromise system integrity Easy to exploit – The attack complexity is low

For businesses, this means:

  • Potential data breaches involving customer information
  • Loss of confidential company data
  • Service outages affecting remote workers
  • Possible compliance violations (GDPR, HIPAA, etc.)

Understanding these risks early is crucial for effective security planning. Organizations can benefit from comprehensive vulnerability intelligence services like those offered by iZOOlogic to stay ahead of emerging threats and maintain robust security postures.

How It Works

Memory overread happens when a program tries to read data from memory locations it shouldn’t access. Think of it like reading someone else’s mail that got mixed in with yours.
In normal operation:

  • NetScaler reads data from its assigned memory space
  • It processes the data and responds appropriately

With this vulnerability:

  • Malicious input tricks NetScaler into reading extra memory
  • This extra memory might contain passwords, tokens, or other sensitive data
  • The attacker can potentially see this leaked information

What You Should Do Right Now

  1. Find your NetScaler systems – Check which ones are configured as Gateway or AAA servers
  2. Apply patches immediately – Citrix released updates on June 17, 2025. Upgrade to:
    • NetScaler ADC and Gateway 14.1-43.56 or later
    • NetScaler ADC and Gateway 13.1-58.32 or later
    • NetScaler ADC 13.1-FIPS/NDcPP 13.1-37.235 or later
    • NetScaler ADC 12.1-FIPS 12.1-55.328 or later

    3. See Citrix Security Bulletin CTX693420 for complete details.

  3. Terminate active sessions – After patching, kill all ICA, PCoIP, and AAA sessions to clear potential exploits
  4. Monitor logs – Look for unusual activity or crashes
  5. Limit access – Restrict network access to NetScaler systems where possible

Temporary Protection

For systems that haven’t been patched yet:
Web Application Firewalls – Filter malformed requests targeting Gateway/AAA endpoints with specific rules Network controls – Limit access to trusted IP addresses via firewalls Monitoring – Deploy intrusion detection systems to spot attack attempts Access restrictions – Add multi-factor authentication where feasible

Important: These are interim measures only. Applying the official patches is the definitive fix and should be the top priority.

What to Watch For

Signs that someone might be exploiting this vulnerability:

  • NetScaler systems crashing unexpectedly
  • Unusual network traffic to NetScaler endpoints
  • Strange entries in authentication logs
  • Abnormal memory usage patterns
  • Failed connection attempts with odd characteristics

Keep detailed logs of:

  • All authentication attempts
  • Network connections to NetScaler
  • System resource usage
  • Any crashes or errors

Lessons Learned

This vulnerability teaches us several important security principles:
Input validation matters – Always validate data before processing it. Proper input checking prevents memory overread attacks Network devices need security too – Don’t assume appliances are automatically secure. They require the same attention as servers Defense in depth works – Multiple security layers help when one component fails Regular updates are critical – Keep systems patched and monitored. End-of-life versions (like NetScaler 12.1 and 13.0) won’t receive security updates Session management is important – Terminating sessions after patching helps clear potential exploits

Timeline

  • June 17, 2025: Vulnerability discovered and assigned CVE-2025-5777; Citrix released patches for both CVE-2025-5777 and CVE-2025-5349
  • June 23, 2025: Details updated in vulnerability databases
  • Current: Patches are available and should be applied immediately

Recommendations

Based on our analysis, here’s what we suggest:

  1. Check your systems now – Use NetScaler logs and configuration files to identify Gateway or AAA server setups
  2. Upgrade End-of-Life versions – Move from NetScaler 12.1 and 13.0 to supported versions that receive security updates
  3. Apply patches immediately – Install the security updates released on June 17, 2025
  4. Terminate active sessions – After patching, kill all ICA, PCoIP, and AAA sessions
  5. Talk to your teams – Make sure IT, security, compliance, and management teams are informed
  6. Document everything – Keep records of affected systems, patch application dates, and monitoring results

CVE-2025-5777 is a critical, easily exploitable flaw in Citrix NetScaler Gateway and AAA servers with a CVSS score of 9.3. Patches are available as of June 17, 2025 apply them immediately, terminate active sessions, and monitor your systems closely.

This incident highlights the importance of timely security updates and layered defense strategies. Organizations using End-of-Life NetScaler versions should prioritize upgrading to supported versions that receive ongoing security patches.

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