CVE-2026-40955 Overview
CVE-2026-40955 is an integer underflow vulnerability [CWE-191] in the traffic parsing function of Absolute Secure Access client software prior to version 14.55. An attacker with intimate knowledge of and total control over the tunnel protocol can send crafted traffic that triggers the underflow and causes a non-persistent denial of service (DoS) against the client. The vulnerability requires network access, high attack complexity, and user interaction, which limits real-world exploitability. Absolute Software has published a security advisory and released a fixed version. No public proof-of-concept exploit is available, and CISA has not added this issue to the Known Exploited Vulnerabilities catalog.
Critical Impact
Successful exploitation causes a non-persistent client-side denial of service in Absolute Secure Access versions before 14.55, temporarily disrupting secure tunnel connectivity until the client restarts.
Affected Products
- Absolute Secure Access client versions prior to 14.55
- Vendor: Absolute Software
- Component: Tunnel traffic parsing function
Discovery Timeline
- 2026-07-15 - CVE-2026-40955 published to NVD
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-40955
Vulnerability Analysis
The flaw resides in the traffic parsing logic of the Absolute Secure Access client. The parser performs arithmetic on a length or offset field derived from tunnel protocol data without validating that the value remains within expected bounds. When a specific manipulated value is processed, the calculation underflows below zero and wraps to a very large unsigned integer. Subsequent memory or buffer operations then use this corrupted length, causing the client process to crash. The condition is non-persistent, meaning the client can recover after restart without state corruption.
Root Cause
The root cause is improper validation of untrusted numeric fields inside the proprietary tunnel protocol before they are used in arithmetic operations. This matches the pattern described in [CWE-191: Integer Underflow (Wrap or Wraparound)]. Because the underflow occurs in code that processes network-supplied protocol data, an attacker who fully controls the tunnel payload can deterministically induce the crash.
Attack Vector
Exploitation requires the attacker to have detailed knowledge of the tunnel protocol and total control over the traffic sent through it. User interaction is also required, and the attack complexity is high because the attacker must position themselves within the tunnel session and craft protocol-conformant data. The result is limited to availability impact on the client. No confidentiality or integrity impact is reported in the advisory.
No verified public exploit code exists for CVE-2026-40955. See the Absolute Security Advisory for vendor-provided technical details.
Detection Methods for CVE-2026-40955
Indicators of Compromise
- Unexpected crashes or abrupt terminations of the Absolute Secure Access client process on endpoints running versions before 14.55.
- Repeated tunnel session drops followed by client reconnection attempts from the same endpoint.
- Malformed tunnel protocol frames observed in network telemetry preceding client termination events.
Detection Strategies
- Monitor endpoint process telemetry for repeated crash events attributed to the Absolute Secure Access client binary.
- Correlate client crash events with inbound tunnel traffic patterns to identify potentially crafted protocol payloads.
- Inventory endpoints and report all Absolute Secure Access installations with versions earlier than 14.55.
Monitoring Recommendations
- Alert on abnormal frequency of Secure Access client restarts across the fleet.
- Track tunnel session reset counts per user and per source to identify targeted disruption attempts.
- Ingest client logs into a centralized logging platform and retain them long enough to correlate with network events.
How to Mitigate CVE-2026-40955
Immediate Actions Required
- Identify all endpoints running Absolute Secure Access clients earlier than version 14.55 and prioritize them for upgrade.
- Apply the vendor-provided update to version 14.55 or later as documented in the Absolute Security Advisory.
- Restrict tunnel endpoints to trusted server infrastructure to reduce exposure to attacker-controlled traffic.
Patch Information
Absolute Software has released Secure Access client version 14.55, which addresses the integer underflow in the traffic parsing function. Administrators should deploy the fixed version through their standard software distribution channels. Refer to the Absolute Security Advisory for the authoritative version guidance.
Workarounds
- No official workaround is published; upgrading to Secure Access 14.55 is the vendor-recommended remediation.
- Limit tunnel connectivity to known, trusted server endpoints to reduce the attack surface until patches are deployed.
- Instruct users to reconnect the Secure Access client if it terminates unexpectedly, since the DoS condition is non-persistent.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
