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Critical Citrix NetScaler memory flaw actively exploited in attacks

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Why This Matters

The active exploitation of the critical CVE-2026-3055 vulnerability in Citrix NetScaler appliances underscores the urgent need for organizations to update their systems. This flaw, which allows attackers to extract sensitive session data and potentially take over affected appliances, highlights the ongoing risks of unpatched enterprise infrastructure. As threat actors rapidly exploit such vulnerabilities, both vendors and users must prioritize timely security updates to mitigate potential breaches.

Key Takeaways

Hackers are exploiting a critical severity vulnerability, tracked as CVE-2026-3055, in Citrix NetScaler ADC and NetScaler Gateway appliances to obtain sensitive data.

Citrix initially disclosed CVE-2026-3055 in a security bulletin on March 23, alongside a high-severity race condition flaw tracked as CVE-2026-4368. The issue impacts versions of the two products before 14.1-60.58, versions older than 13.1-62.23, and those older than 13.1-37.262.

The vendor underlined that the flaw only affected appliances configured as a SAML identity provider (IDP) and noted that action is required only for administrators running on-premise appliances.

In response to the bulletin, multiple cybersecurity firms highlighted that CVE-2026-3055 has a significant risk, noting technical resemblance to the widely exploited ‘CitrixBleed’ and CitrixBleed2’ from 2023 and 2025, respectively.

watchTowr, a company that provides adversarial simulation and continuous testing services, said on Saturday that it observed reconnaissance activity targeting vulnerable instances and warned that in-the-wild exploitation was imminent.

The next day, the researchers confirmed that threat actors started leveraging the flaw since at least March 27.to extract authentication administration session IDs, potentially enabling a full takeover of NetScaler appliances.

“In-the-wild exploitation has begun, with evidence from our honeypot network showing exploitation from known threat actor source IPs as of March 27th,” reports watchTowr.

watchTowr’s analysis indicates that CVE-2026-3055 actually covers at least two distinct memory overread bugs, not one. The first affects the ‘/saml/login’ endpoint handling SAML authentication, while the second one affects the ‘/wsfed/passive’ endpoint used for WS-Federation passive authentication.

The researchers demonstrated that the security flaw can be leveraged to "sensitive information - including authenticated administrative session IDs."

Leaking Session ID from memory

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