Citrix NetScaler ADC and Gateway Out-of-Bounds Read
CVE-2025-5777 is a high-severity use of uninitialized resource vulnerability in ADC from NetScaler, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 43.56, 58.32 as the first without the flaw, so updating ADC to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on July 10, 2025, which means attacks have been observed in the wild, including in ransomware campaigns.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update ADC to 43.56 or 58.32, whichever matches your release line, or a later version.
- Update Gateway to 43.56 or 58.32, whichever matches your release line, or a later version.
- Update Netscaler Application Delivery Controller to 12.1-55.328 or 13.1-37.235 or 13.1-58.32 or 14.1-43.56, whichever matches your release line, or a later version.
- CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- Read the advisory on support.citrix.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| NetScaler | ADC | 14.1 up to, but not including, 43.56; 13.1 up to, but not including, 58.32 | 43.56, 58.32 |
| NetScaler | Gateway | 14.1 up to, but not including, 43.56; 13.1 up to, but not including, 58.32 | 43.56, 58.32 |
| Citrix | Netscaler Application Delivery Controller | 12.1 up to, but not including, 12.1-55.328; 13.1 up to, but not including, 13.1-37.235; 13.1 up to, but not including, 13.1-58.32; 14.1 up to, but not including, 14.1-43.56 | 12.1-55.328, 13.1-37.235, 13.1-58.32, 14.1-43.56 |
| Citrix | Netscaler Gateway | 13.1 up to, but not including, 13.1-58.32; 14.1 up to, but not including, 14.1-43.56 | 13.1-58.32, 14.1-43.56 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA (citrix.com) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Insufficient input validation leading to memory overread when the NetScaler is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Uninitialized Resource
The product uses or accesses a resource that has not been initialized.
How developers prevent this class of flaw
- Explicitly initialize the resource before use. If this is performed through an API function or standard procedure, follow all required steps.
- Pay close attention to complex conditionals that affect initialization, since some branches might not perform the initialization.
- Avoid race conditions (CWE-362) during initialization routines.
More Use of Uninitialized Resource vulnerabilities (CWE-908)
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- horizon3.ai/attack-research/attack-blogs/cve-2025-5777-citrixbleed-2-write-up-maybe/Third Party Advisory
- labs.watchtowr.com/how-much-more-must-we-bleed-citrix-netscaler-memory-disclosure-citrixbleed-2-cve-2025-5777/Third Party Advisory
- bleepingcomputer.com/news/security/cisa-tags-citrix-bleed-2-as-exploited-gives-agencies-a-day-to-patch/Press/Media Coverage, Third Party Advisory
- netscaler.com/blog/news/netscaler-critical-security-updates-for-cve-2025-6543-and-cve-2025-5777/Third Party Advisory
- doublepulsar.com/citrixbleed-2-exploitation-started-mid-june-how-to-spot-it-f3106392aa71Third Party Advisory
- reliaquest.com/blog/threat-spotlight-citrix-bleed-2-vulnerability-in-netscaler-adc-gateway-devices/Third Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-5777US Government Resource
Other references
- theregister.com/2025/07/10/cisa_citrixbleed_kev/Press/Media Coverage
Other vulnerabilities in ADC
- 9.5 Critical severity
- 7.5 High severity
- 9.8 Critical severity
- 8.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
Recent Use of Uninitialized Resource vulnerabilities
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
- 7.8 High severity
- 9.8 Critical severity
- 9.8 Critical severity
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