New CitrixBleed Vulnerability Exploited Immediately After Public Disclosure

Summary

Threat actors began exploiting CVE-2026-8451, a critical out-of-bounds read vulnerability in Citrix NetScaler ADC and Gateway appliances, less than 24 hours after Citrix released patches and watchTowr published technical details on June 30. The vulnerability allows unauthenticated attackers to retrieve arbitrary memory content from appliances configured as SAML IDP, with at least two threat actors observed probing and delivering payloads to exposed instances. Organizations are advised to patch immediately or disable SAML IDP, and monitor logs for /saml/login traffic and NSC_TASS cookie values.

Full text

Threat actors began exploiting the latest CitrixBleed-like vulnerability in NetScaler ADC and NetScaler Gateways less than 24 hours after public disclosure, Scottish cybersecurity firm Lupovis reports. Tracked as CVE-2026-8451 (CVSS score of 8.8), the security defect was disclosed on June 30, when Citrix rolled out patches, and attack surface management company watchTowr published technical details on it. The bug is described as an out-of-bounds read issue affecting NetScaler appliances configured as SAML IDP and leading to memory disclosure. It was discovered in NetScaler’s XML parser, which did not terminate unquoted XML attribute values if they were followed by a newline character. Because of the flaw, the parser would read past the intended buffer, and NetScaler would return memory contents in the NSC_TASS cookie in an HTTP response. While it requires that the targeted NetScaler appliances be configured as SAML IDP, the successful exploitation of the vulnerability does not require authentication. Shortly after watchTowr shared details on the security hole and published a detection artefact generator, at least one threat actor started probing exposed NetScaler instances, Lupovis told SecurityWeek.Advertisement. Scroll to continue reading. Initial scanning activity originated from an IP hosted on infrastructure in Frankfurt, Germany, likely using a disposable or purpose-built scanning node. Multiple Lupovis sensors were targeted within a five-hour window, and a payload was immediately dropped on the sensor that responded with a 200 response. The payload included a “bare <samlp:AuthnRequest> tag padded with 476 spaces followed by a newline”, which matches the overread variant in watchTowr’s detection artefact generator. On Thursday, the cybersecurity firm observed a second threat actor probing for exposed NetScaler instances from a Koapu Cloud HK IP address. “Both have demonstrated the same behaviour, probing for the right endpoint, upon receiving a 200 OK with the right response, they have delivered the payload immediately,” Lupovis CEO Xavier Bellekens said. Organizations are advised to patch their NetScaler appliances immediately, or to disable SAML IDP if patching is not possible. They should also check logs for /saml/login traffic, inspect the request values, and check NSC_TASS cookie values to identify exploitation. 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Indicators of Compromise

• cve — CVE-2026-8451

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