CVE-2025-39849: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-39849 is an out-of-bounds write vulnerability in the Linux kernel's cfg80211 SME (Station/Supplicant Mode Engine) module, specifically in the __cfg80211_connect_result() function. When an SSID's datalen field exceeds IEEE80211_MAX_SSID_LEN (32 bytes), insufficient bounds checking leads to kernel memory corruption. The vulnerability was disclosed on September 19, 2025, and affects Linux kernel versions 6.1.16–6.1.150, 6.2.3–6.6.104, 6.7–6.12.45, and 6.13–6.16.5, as well as release candidates 6.17-rc1 through 6.17-rc4. It carries a CVSS v3.1 base score of 7.8 (High) (Red Hat CVE, Red Hat Bugzilla).

The root cause is classified as CWE-787 (Out-of-bounds Write). The __cfg80211_connect_result() function in the kernel's wireless configuration subsystem (net/wireless/sme.c) processes SSID data returned during Wi-Fi connection results without enforcing the maximum SSID length of 32 bytes (IEEE80211_MAX_SSID_LEN). If a crafted or malformed SSID with a datalen exceeding this limit is processed, the kernel writes beyond the allocated buffer boundary, resulting in heap or stack memory corruption. The fix adds explicit bounds checking to cap the SSID length before any memory operations are performed (Red Hat Bugzilla, Red Hat CVE). The attack vector is local, requiring low privileges and no user interaction.

Successful exploitation by a locally authenticated low-privileged attacker can result in kernel memory corruption, potentially leading to arbitrary code execution in kernel context, system crashes (denial of service), or information disclosure. The vulnerability has HIGH impact on confidentiality, integrity, and availability. In practice, an attacker could leverage this to escalate privileges or destabilize the system, and affected platforms include standard Linux distributions (RHEL 8/9/10, Ubuntu, AlmaLinux, Rocky Linux, Oracle Linux, Debian 11) as well as IBM Netezza Appliance and Microsoft Azure Linux 3 (Red Hat CVE, IBM Advisory).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation at this time (Red Hat CVE). The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.018% (0.000180), indicating a very low probability of exploitation in the near term. Exploitation requires local access with low privileges, which limits the attack surface compared to remotely exploitable vulnerabilities.

Apply the available kernel patches immediately. Fixed kernel versions include 6.1.151, 6.6.105, 6.12.46, and 6.16.6 or later, with commits available in the stable kernel tree (Red Hat Bugzilla). Red Hat has issued errata for RHEL 8 (RHSA-2025:19102, RHSA-2025:19103), RHEL 9 (RHSA-2025:18281, RHSA-2025:21112, RHSA-2025:21760), and RHEL 10 (RHSA-2025:19106, RHSA-2025:21118). Ubuntu security notices USN-8095-1 through USN-8095-5, USN-8100-1, USN-8125-1, and USN-8165-1 also address this issue. As interim mitigations, restrict local system access to trusted users only, enable kernel ASLR (KASLR) and stack canary protections, and monitor for unexpected kernel crashes or memory corruption errors.