Uninitialized data
A program uses memory before the required value has been set.
CWE-908 · NVD record: nvd@nist.gov
Video course · Free course. C programming and memory concepts are useful; covers several weakness types.
Exploited. On CISA's list since 2025-07-10, and used by ransomware.
Citrix NetScaler ADC and Gateway Out-of-Bounds Read Vulnerability
CVE-2025-5777 · Citrix NetScaler ADC and Gateway · Published 2025-06-17
How bad would it be?
9.3 out of 10
CVSS rates it critical: about as damaging as flaws get.
How likely is it to be used?
over 99%
Estimated chance of exploitation in the next 30 days, among the top 1% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 476 days ago (2025-07-11).
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Citrix NetScaler ADC and Gateway contain an out-of-bounds read vulnerability due to insufficient input validation. This vulnerability can lead to memory overread when the NetScaler is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server.
What the flaw is
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
From the NVD.
Fixes and advisories
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Explore this week’s weaknesses and all learning topics
Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
CWE-125 · CISA KEV; NVD record: secure@citrix.com. We have not selected a close learning match for this label.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.