CVE-2026-40955 in Secure Access
Summary
by MITRE • 07/15/2026
CVE-2026-40955 is an integer underflow vulnerability in the traffic parsing function of Secure Access clients prior to 14.55. Attackers with intimate knowledge of and total control over the tunnel protocol can create a non-persistent DoS against their client.
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Analysis
by VulDB Data Team • 07/15/2026
The integer underflow vulnerability identified as CVE-2026-40955 represents a critical flaw in the traffic parsing functionality of Secure Access clients version 14.54 and earlier. This vulnerability stems from improper input validation within the client's network protocol handling mechanism, specifically when processing tunnel protocol data. The flaw manifests when the system attempts to perform arithmetic operations on integer values that fall below their minimum representable range, causing the value to wrap around to a large positive number instead of properly handling the underflow condition. This type of vulnerability falls under CWE-191, which specifically addresses integer underflows where an operation results in a value smaller than the minimum representable value for the data type involved.
The operational impact of this vulnerability is significant within environments where attackers possess intimate knowledge of the tunnel protocol and maintain complete control over communication channels. The attacker can craft malicious traffic packets that specifically trigger the integer underflow condition during the parsing process, leading to a denial-of-service state that affects the client application's ability to process legitimate network traffic. This non-persistent DoS attack does not require persistent access to the system but rather relies on precise timing and protocol manipulation to exploit the vulnerability effectively. The attack vector specifically targets the client-side processing components, making it particularly dangerous in scenarios where clients are deployed in critical network infrastructure or remote access environments.
The technical exploitation of this vulnerability requires a deep understanding of both the Secure Access client implementation and the underlying tunnel protocol specifications. Attackers must be able to craft packets that will cause integer underflow during traffic parsing operations, typically by manipulating sequence numbers, packet lengths, or other numeric fields within the protocol headers. This attack pattern aligns with ATT&CK technique T1498.001, which involves network denial-of-service attacks, and represents a sophisticated approach to disrupting network connectivity through protocol-level manipulation rather than traditional network flooding methods. The vulnerability's classification as non-persistent indicates that it does not create lasting changes to the system state but instead causes temporary disruption that requires client restart or intervention to resolve.
Organizations should prioritize immediate patching of affected Secure Access clients to version 14.55 or later, which contains the necessary fixes for this integer underflow condition. Network administrators should implement monitoring solutions that can detect anomalous traffic patterns potentially indicative of exploitation attempts, particularly focusing on unusual packet structures that might trigger integer underflows. The mitigation strategy should include network segmentation to limit potential attack surface and implementing protocol validation mechanisms that can detect and drop malformed packets before they reach vulnerable parsing functions. Additionally, security teams should conduct thorough vulnerability assessments of all client endpoints to identify systems running affected versions and establish incident response procedures specifically tailored to address this type of protocol-level denial-of-service attack.