Citrix NetScaler Out-of-Bounds Read
CVE-2026-3055 is a critical-severity out-of-bounds read vulnerability in ADC from NetScaler, with a CVSS 3.1 base score of 9.8 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 66.59, 62.23, 37.262 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 March 30, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update ADC to 66.59 or 62.23 or 37.262, whichever matches your release line, or a later version.
- Update Gateway to 66.59 or 62.23, whichever matches your release line, or a later version.
- Update Netscaler Application Delivery Controller to 13.1-37.262 or 13.1-62.23 or 14.1-60.58, 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, 66.59; 13.1 up to, but not including, 62.23; 13.1 FIPS and NDcPP up to, but not including, 37.262 | 66.59, 62.23, 37.262 |
| NetScaler | Gateway | 14.1 up to, but not including, 66.59; 13.1 up to, but not including, 62.23 | 66.59, 62.23 |
| Citrix | Netscaler Application Delivery Controller | 13.1 up to, but not including, 13.1-37.262; 13.1 up to, but not including, 13.1-62.23; 14.1 up to, but not including, 14.1-60.58 | 13.1-37.262, 13.1-62.23, 14.1-60.58 |
| Citrix | Netscaler Gateway | 13.1 up to, but not including, 13.1-62.23; 14.1 up to, but not including, 14.1-60.58 | 13.1-62.23, 14.1-60.58 |
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
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.3 | Critical | CNA |
| CVSS 3.1 | 9.8 | Critical | NVD |
Official description
Insufficient input validation in NetScaler ADC and NetScaler Gateway when configured as a SAML IDP leading to memory overread
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that provides appropriate memory abstractions.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-3055US Government Resource
Technical write-ups (may include proof of concept)
- labs.watchtowr.com/please-we-beg-just-one-weekend-free-of-appliances-citrix-netscaler-cve-2026-3055-memory-ov…Exploit, Third Party Advisory
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 Out-of-bounds Read vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
- 8.8 High severity
- 8.8 High severity
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