# CVE-2023-4966 (Citrix Bleed): Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow

> Unauthenticated attackers can disclose sensitive session data from Citrix NetScaler ADC and Gateway when configured as a Gateway or AAA virtual server.

- **Severity:** Critical 9.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L`)
- **Exploited in the wild:** Yes, since 18 Oct 2023 (CISA KEV), used in ransomware
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 10 Oct 2023
- **Updated:** 31 Jul 2026
- **Also known as:** GHSA-2g42-2pwg-93cj

## What is CVE-2023-4966?

CVE-2023-4966 (Citrix Bleed) is a critical vulnerability in Citrix NetScaler ADC, published on 10 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Sensitive information disclosure in NetScaler ADC and NetScaler Gateway when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA  virtual server.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2023-4966?

It affects 2 products.


Products: Citrix NetScaler ADC, Citrix Netscaler Gateway.

## How do I fix CVE-2023-4966?

No fix has been published for CVE-2023-4966 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 8 Nov 2023.

## Is CVE-2023-4966 being exploited?

Yes. Attackers have exploited CVE-2023-4966 in the wild since at least 18 Oct 2023, including in ransomware campaigns.

Public exploit code:

- Sensitive information disclosure in NetScaler ADC and NetScaler Gateway when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.  (github_poc): https://github.com/Chocapikk/CVE-2023-4966
- Citrix CVE-2023-4966 from assetnote modified for parallel and file handling (github_poc): https://github.com/dinosn/citrix_cve-2023-4966
- An Exploitation script developed to exploit the CVE-2023-4966 bleed citrix information disclosure vulnerability (github_poc): https://github.com/RevoltSecurities/CVE-2023-4966
- Proof Of Concept for te NetScaler Vuln (github_poc): https://github.com/mlynchcogent/CVE-2023-4966-POC
- Parse citrix netscaler logs to check for signs of CVE-2023-4966 exploitation (github_poc): https://github.com/certat/citrix-logchecker
- Simulates CVE-2023-4966 Citrix Bleed overread bug (github_poc): https://github.com/morganwdavis/overread

## Other vulnerabilities in Citrix NetScaler ADC

- [CVE-2023-3519](https://insights.sbomify.com/CVE-2023-3519/): Citrix NetScaler ADC and NetScaler Gateway Code Injection (critical 9.8, exploited in the wild)
- [CVE-2026-88771](https://insights.sbomify.com/CVE-2026-88771/): Citrix NetScaler Improper Input Validation (critical 9.5, exploited in the wild)
- [CVE-2026-88772](https://insights.sbomify.com/CVE-2026-88772/): Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer (critical 9.5, exploited in the wild)
- [CVE-2026-19490](https://insights.sbomify.com/CVE-2026-19490/): Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel (critical 9.3, exploited in the wild)
- [CVE-2026-3055](https://insights.sbomify.com/CVE-2026-3055/): Citrix NetScaler Out-of-Bounds Read (critical 9.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-4966 (Citrix Bleed) and fix it if it is affected.

What it is: CVE-2023-4966 (Citrix Bleed) is a critical vulnerability in Citrix NetScaler ADC, published on 10 Oct 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2023-4966 in the wild since at least 18 Oct 2023, including in ransomware campaigns.

Affected product: Citrix NetScaler ADC. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-4966/ (Markdown: https://insights.sbomify.com/CVE-2023-4966/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-4966
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-4966
- OSV: https://osv.dev/vulnerability/CVE-2023-4966

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-4966/
Summaries are generated and may contain mistakes; the official description above is the record.