Citrix ADC zero-day exploitation: CISA releases details about attack on CI organization (CVE-2023-3519)
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-3519 | Unauthenticated RCE in Citrix NetScaler ADC and NetScaler Gateway CVE-2023-3519 is a critical (CVSS 9.8) unauthenticated remote code execution flaw caused by improper code-injection handling (CWE-94) in Citrix NetScaler ADC and NetScaler Gateway. A remote attacker with no credentials can trigger it by sending crafted requests to an appliance configured as a Gateway (VPN/ICA proxy/RDP proxy) or AAA authentication virtual server, gaining arbitrary code execution on the appliance. Exploitation typically yields a foothold behind the VPN edge — access to internal networks, credential theft, and follow-on activity such as espionage or ransomware deployment. Any organization running unpatched NetScaler ADC/Gateway appliances, especially internet-facing remote-access endpoints, is affected; NetScaler is one of the most widely deployed enterprise VPN/ADC platforms. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV on 2023-07-19 with known ransomware use, EPSS estimates a 99.7% exploitation probability, and researchers have linked activity to China-nexus espionage (Silk Typhoon) and ransomware operations. Do: Immediately upgrade internet-facing NetScaler ADC/Gateway appliances to the fixed builds in Citrix's advisory (14.1-8.50+, 13.1-49.13+, 13.0-82.45+, 12.1-55.300+, including FIPS/NDcPP equivalents) — per CISA KEV, apply these mitigations or discontinue use if patching is unavailable. Confirm whether each appliance is configured as a Gateway or AAA virtual server (only those are affected), and hunt for compromise — unexpected configuration changes, unfamiliar accounts, webshells, or anomalous VPN sessions — rotating credentials on any suspected compromise. | 9.8 | 100% | KEV ransomware PoC |
| largetens of thousands of internet-exposed NetScaler Gateway/ADC appliances (order 10k-100k at disclosure), serving hundreds of thousands to millions of downstream… |
Full article473 words · extracted from helpnetsecurity.com · click to collapse
The exploitation of the Citrix NetScaler ADC zero-day vulnerability (CVE-2023-3519) was first spotted by a critical infrastructure organization, who reported it to the Cybersecurity and Infrastructure Security Agency (CISA).
“In June 2023, threat actors exploited this vulnerability as a zero-day to drop a webshell on a critical infrastructure organization’s non-production environment NetScaler ADC appliance. The webshell enabled the actors to perform discovery on the victim’s active directory (AD) and collect and exfiltrate AD data. The actors attempted to move laterally to a domain controller but network-segmentation controls for the appliance blocked movement,” the agency shared in an advisory published on Thursday.
IoCs, IR and mitigation advice
The attack was reported to CISA and Citrix in July 2023, and Citrix announced fixes for it on July 18.
The security bulletin mentioned that “exploits of CVE-2023-3519 on unmitigated appliances have been observed,” but no additional details about the attacks or how to check whether an organizations had been a target had been publicly shared.
A list of indicators of compromise (IoCs) had been shared with select organizations, under the understanding that the info would not be widely shared (i.e., that the contents would be restricted to those organization and shared with its clients “on a need-to-know basis”).
“As we hear from the Citrix community, more and more attacked systems are being found. The first exploits have also been available for purchase on the dark web for some time,” German IT consultant Manuel Winkel said on July 19.
He shared advice on how to check whether one’s organization has been hit, and advised on what to do if the result is positive.
CISA’s advisory offers more details about the threat actor activity in the attack detected at the critical infrastructure organization, delineates attack detection methods, and offers advice on incident response if compromise is detected.
In-the-wild exploitation of CVE-2023-3519
Greynoise has created a tag to show in-the-wild probing of internet-facing NetScaler ADC platforms and Gateways with authentication attempts through CVE-2023-3519, but so far there have been no detections.
Standalone and Nmap scripts for identifying vulnerable installations have been published on GitHub.
If what Winkel says is true – namely, that first exploits for CVE-2023-3519 have been available for purchase on the dark web for a while – it’s possible that there are many compromised organizations out there who didn’t manage to block the attackers’ lateral movement.
It’s currently impossible to say what the attackers’ ultimate goal is, but affected organizations may discover it soon if they don’t react quickly.
UPDATE (July 22, 2023, 10:55 a.m. ET):
Technical analyses of the flaw are now public and threat actors could use them to create a reliable exploit soon. Patch quickly!
Based on their analysis of a compromised appliance, Mandiant has also published their own findings related to in-the-wild attacks, along with remediation, hardening, and threat hunting advice.
Text extracted automatically; images, tables and formatting may be missing. Original: https://www.helpnetsecurity.com/2023/07/21/cve-2023-3519-exploitation/