Critical CitrixBleed 2 vulnerability has been under active exploit for weeks
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-4966 | Info-Disclosure Buffer Overflow (CitrixBleed) in Citrix NetScaler ADC/Gateway Citrix NetScaler ADC and NetScaler Gateway appliances contain a buffer overflow (CWE-119) that leaks sensitive information from device memory when the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server. A remote attacker who can reach such a configuration can trigger the overflow and read memory contents, harvesting sensitive data such as session tokens (a technique that enables session hijacking which can bypass multi-factor authentication). Any organization running an affected NetScaler ADC or Gateway appliance in these configurations is exposed, with appliances deployed as VPN or access gateways being the primary concern. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV catalog on 2023-10-18 with known ransomware use and a 100% EPSS exploitation probability, although no public proof-of-concept is known at this time. Because tokens stolen from memory can remain valid even after patching, responders must terminate all active and persistent sessions as part of remediation. Do: Upgrade affected appliances to the patched builds cited in Citrix's advisory, then immediately kill all active and persistent ICA/AAA sessions per the vendor instructions, since patching alone does not invalidate session tokens attackers may have already stolen. If patching is not immediately possible, discontinue use of the affected Gateway/AAA configurations as CISA directs. Given known ransomware abuse, also hunt for signs of exploitation such as logins from unexpected sources, anomalous session reuse, or suspicious mailbox changes, and reset credentials for potentially exposed accounts. | 7.5 | 100% | KEV ransomware |
| masshundreds of thousands of internet-exposed NetScaler ADC/Gateway appliances (public internet scan counts), plus an unknown number of VPN-only or internal… | |
| CVE-2025-5777 | Out-of-Bounds Read (Memory Overread) in Citrix NetScaler ADC and Gateway Citrix NetScaler ADC and NetScaler Gateway contain an out-of-bounds read (CWE-125) caused by insufficient input validation, which can cause the appliance to read beyond the intended memory buffer (a memory overread). The flaw is only triggerable when the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server, so attackers who can reach those services can potentially induce the overread and obtain sensitive memory contents. Such disclosure could aid follow-on compromise, for example by exposing session or authentication data, and CISA notes known ransomware use. Organizations running NetScaler ADC or NetScaler Gateway in the affected Gateway/AAA configurations are exposed. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2025-07-10 with known ransomware use and an EPSS of 100% (100th percentile), indicating active exploitation, while no public PoC is known and a CVSS score has not yet been assigned. Do: Apply the fixed NetScaler ADC/Gateway builds per Citrix's security advisory (exact affected/fixed version ranges are not in the available data, so consult the bulletin); per CISA KEV, apply vendor mitigations, follow BOD 22-01 guidance for cloud services, or discontinue use if mitigations are unavailable. Inventory appliances for Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server configurations, since unconfigured/other deployments are not triggerable. After patching, terminate active and idle VPN sessions and hunt for anomalous access, given the known ransomware exploitation and the information-disclosure nature of the flaw. | 9.3 | 100% | KEV ransomware |
| massplausibly hundreds of thousands of installed/internet-exposed NetScaler ADC and Gateway appliances (public scans have historically shown on the order of… |
Full article402 words · extracted from arstechnica.com · click to collapse
A critical vulnerability allowing hackers to bypass multifactor authentication in network management devices made by Citrix has been actively exploited for more than a month, researchers said. The finding is at odds with advisories from the vendor saying there is no evidence of in-the-wild exploitation.
Tracked as CVE-2025-5777, the vulnerability shares similarities with CVE-2023-4966, a security flaw nicknamed CitrixBleed, which led to the compromise of 20,000 Citrix devices two years ago. The list of Citrix customers hacked in the CitrixBleed exploitation spree included Boeing, Australian shipping company DP World, Commercial Bank of China, and the Allen & Overy law firm. A Comcast network was also breached, allowing threat actors to steal password data and other sensitive information belonging to 36 million Xfinity customers.
Giving attackers a head start
Both CVE-2025-5777 and CVE-2023-4966 reside in Citrix’s NetScaler Application Delivery Controller and NetScaler Gateway, which provide load balancing and single sign-on in enterprise networks, respectively. The vulnerability causes vulnerable devices to leak—or “bleed”—small chunks of memory contents after receiving modified requests sent over the Internet.
By repeatedly sending the same requests, hackers can piece together enough data to reconstruct credentials. The original CitrixBleed had a severity rating of 9.8. CitrixBleed 2 has a severity rating of 9.2.
Citrix disclosed the newer vulnerability and released a security patch for it on June 17. In an update published nine days later, Citrix said it was “currently unaware of any evidence of exploitation.” The company has provided no updates since then.
Researchers, however, say that they have found evidence that CitrixBleed 2, as the newer vulnerability is being called, has been actively exploited for weeks. Security firm Greynoise said Monday that a search through its honeypot logs found exploitation as early as July 1. On Tuesday, independent researcher Kevin Beaumont said telemetry from those same honeypot logs indicates that CitrixBleed 2 has been exploited since at least June 23, three days before Citrix said it had no evidence of such attacks.
Citrix’s failure to disclose active exploitation is only one of the details researchers say was missing from the advisories. Last week, security firm watchTowr published a post titled “How Much More Must We Bleed? – Citrix NetScaler Memory Disclosure (CitrixBleed 2 CVE-2025-5777).” It criticized Citrix for withholding indicators that customers could use to determine if their networks were under attack. On Monday, fellow security firm Horizon3.ai said much the same thing. Company researchers wrote:
Text extracted automatically; images, tables and formatting may be missing. Original: https://arstechnica.com/security/2025/07/critical-citrixbleed-2-vulnerability-has-been-under-active-exploit-for-weeks/