CVE-2026-59840: 
FortiOS Analyse et atténuation des vulnérabilités

CVE-2026-59840 is a buffer over-read vulnerability (CWE-126) in Fortinet FortiOS, FortiProxy, and FortiSASE that may allow an authenticated remote attacker to return a portion of device memory via a specially crafted request. Affected versions include FortiOS 7.6.0–7.6.2, 7.4.0–7.4.8, and 7.2 (all versions); FortiProxy 7.6.0–7.6.5, 7.4.0–7.4.13, and 7.2 (all versions). The vulnerability was publicly disclosed on July 14, 2026, and carries a CVSSv3.1 base score of 4.1–4.3 (Medium) (FortiGuard Advisory, Feedly).

The root cause is a buffer over-read (CWE-126) in the authd and wad daemons of FortiOS and FortiProxy. An authenticated attacker can submit a specially crafted request that causes the affected daemon to include adjacent memory contents in the redirect response, potentially leaking sensitive in-memory data. Exploitation requires low-level authenticated access over the network (no user interaction required), and the attack vector is network-based with low complexity (FortiGuard Advisory). No public proof-of-concept code has been identified at this time (Feedly).

Successful exploitation results in partial information disclosure — specifically, a portion of device memory may be returned to the attacker in a redirect response. The confidentiality impact is low, with no integrity or availability impact. While the leaked memory could potentially contain sensitive configuration data, credentials, or session tokens, the scope is limited to the affected device and does not directly enable lateral movement or remote code execution (FortiGuard Advisory, Feedly).

Fortinet has released patched versions to address this vulnerability. Users should upgrade to the following fixed releases: FortiOS 7.6.4 or above (for 7.6.x), FortiOS 7.4.9 or above (for 7.4.x), and FortiOS 7.2 users should migrate to a fixed release. For FortiProxy, upgrade to 7.6.6 or above (for 7.6.x) or 7.4.14 or above (for 7.4.x); FortiProxy 7.2 users should migrate to a fixed release. A virtual patch named FG-VD-58646.0day is also available in FMWP database update 26.010 for environments that cannot immediately upgrade. Fortinet recommends using the official upgrade path tool at https://docs.fortinet.com/upgrade-tool and restricting management interface access to trusted administrators only (FortiGuard Advisory).

The vulnerability was reported to Fortinet by Vang3lis and Cyth from VARAS@IIE under responsible disclosure, and Fortinet acknowledged their contribution in the official advisory. No significant broader media coverage or notable researcher commentary beyond the initial disclosure has been identified at this time (FortiGuard Advisory).