Microsoft Patch Tuesday, September 2025 Edition

CVE-2025-38352 is a time-of-check to time-of-use (TOCTOU) race condition (CWE-367) in the Linux kernel's POSIX CPU timers subsystem: when an exiting non-auto-reaping task has passed exit_notify() and handles CPU timers from interrupt context, it can be reaped by its parent or debugger right after unlock_task_sighand(), so a concurrent posix_cpu_timer_del() cannot detect that the timer is firing (cpu_timer_task_rcu() and/or lock_task_sighand() fail). A local attacker with low privileges who can manipulate POSIX CPU timers on such a task can win this race window, with high impact to confidentiality, integrity, and availability (CVSS 3.1: 7.8, local vector, no user interaction). Any system running an affected Linux kernel is exposed, including Debian GNU/Linux deployments and Android devices built on the kernel; practical reachability is limited where CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y routes timer handling through task work instead of IRQ context. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2025-09-04 and Google shipped it as an actively exploited fix in the September 2025 Android security update; EPSS currently estimates a 1.3% probability of exploitation within 30 days (68th percentile), and a public proof-of-concept is available.

Do: Apply updated kernel packages from your distribution (Debian and other vendors ship the upstream posix-cpu-timers fix) and install Google's September 2025 Android security patch on Android devices; CISA KEV listing requires federal agencies to apply vendor mitigations or discontinue use per BOD 22-01. Because exploitation requires local code execution, prioritize multi-tenant servers, build/CI hosts, and devices where untrusted users or apps run local code. A public proof-of-concept (github.com/farazsth98/chronomaly) is available for validation testing.

CVE-2025-43300 is an out-of-bounds write (CWE-787) in the Image I/O (ImageIO) framework used by Apple iOS, iPadOS, and macOS. It can be triggered when a device processes a specially crafted image file, corrupting memory in the image-parsing process. Successful exploitation may cause application crashes or allow arbitrary code execution with the privileges of the application handling the image. Because ImageIO is a core system component on essentially every Apple device, virtually all users of iPhones, iPads, and Macs are exposed. The flaw is being exploited in the wild — CISA added it to the KEV catalog on 2025-08-21, mandating patching per BOD 22-01 for federal agencies — and EPSS estimates a 22% probability of exploitation in the next 30 days (98th percentile); no public PoC is known and ransomware use is unconfirmed.

Do: Apply Apple's security updates for iOS, iPadOS, and macOS issued in August 2025 (e.g., iOS 18.6.1 / iPadOS 18.6.1 and macOS Sequoia 15.6.1) on all devices, prioritizing user-facing fleets and agencies bound by BOD 22-01 deadlines. Until devices are patched, exercise caution with images from untrusted sources (email, messaging, web content), since no compensating mitigations are specified. Note that the source data does not enumerate exact affected builds, so verify coverage against Apple's advisory and CISA KEV required actions.

CVE-2025-48543 is a use-after-free (CWE-416) in the Android Runtime that exists in multiple code locations and allows an attacker who has already achieved code execution inside the Chrome sandbox to escape and attack the Android system_server process. The trigger requires only local access to the vulnerable component, with no additional execution privileges and no user interaction needed for exploitation. A successful attacker gains local escalation of privilege in the Android system server, making the bug especially useful as a privilege-escalation link in exploit chains against Android devices. Any Android device from Google's platform is in scope per CISA's listing (vendor: Google, product: Android, component: Android Runtime); specific affected version ranges are not enumerated in the source data. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2025-09-04 and Google's related headlines indicate it is being actively exploited in the wild; EPSS currently estimates only a 0.5% probability of exploitation in the next 30 days, and ransomware use is listed as unknown.

Do: Apply Google's Android security updates (September 2025 security bulletin patch level or later) as soon as they are available for your devices, since this flaw is listed in CISA's KEV and reported as exploited in the wild; per KEV required action, federal agencies must follow BOD 22-01 timelines or discontinue use if mitigations are unavailable. Use MDM/EDR tooling to verify device security patch levels, and note that because this is a sandbox-escape-to-system_server bug, it is most dangerous when chained with a browser/renderer exploit, so keeping Chrome/WebView current matters as well.

CVE-2025-55234 is an improper authentication flaw (CWE-287) in the Microsoft SMB Server that leaves systems susceptible to credential relay attacks when SMB signing and Extended Protection for Authentication (EPA) are not enforced. It is configuration-dependent: an attacker who can induce an authenticated SMB connection, for example by tricking a user or machine into connecting to attacker-controlled resources, can relay the credentials to another host and authenticate as that user. Successful relaying grants the attacker the privileges of the relayed user, up to elevation of privilege on target systems, with high impact on confidentiality, integrity and availability. Affected systems span Windows 10 (1507 through 22H2), Windows 11 (22H2 through 24H2), and Windows Server 2008, 2012, 2016 and 2019, although only environments without SMB signing/EPA hardening are practically exploitable. As of the September 2025 Patch Tuesday release there is no known in-the-wild exploitation or public proof of concept, but EPSS assigns a 20.1% probability of exploitation within the next 30 days (97th percentile).

Do: Install the September 2025 (or later) Microsoft security updates, which add SMB Server Hardening audit capabilities, and use the new audit events to identify clients, servers or legacy software that would break if SMB signing and EPA are enforced. After remediating incompatibilities, enable SMB Server signing and Extended Protection for Authentication on SMB servers to close the relay exposure, prioritizing domain controllers and file servers. Note that systems already enforcing both signing and EPA are not practically exposed.

CVE-2025-55177 is an incorrect authorization flaw (CWE-863) in how WhatsApp for iOS, WhatsApp Business for iOS, and WhatsApp for Mac validate linked device synchronization messages, allowing an unrelated user to trigger processing of content from an arbitrary URL on a target's device. An attacker can reach a vulnerable client through the messaging channel without normal authorization checks, causing the app to fetch or process attacker-chosen content. On its own the flaw carries only partial confidentiality and integrity impact (CVSS 5.4), but Meta assesses it was chained with an Apple OS vulnerability (CVE-2025-43300) in a sophisticated attack against specific, targeted users. Users running WhatsApp for iOS before 2.25.21.73, WhatsApp Business for iOS before 2.25.21.78, or WhatsApp for Mac before 2.25.21.78 are affected. The flaw was added to CISA's KEV catalog on 2025-09-02 amid reports of highly targeted zero-day attacks, though no public proof-of-concept is known and use in ransomware campaigns has not been reported.

Do: Update WhatsApp for iOS to v2.25.21.73 or later, WhatsApp Business for iOS to v2.25.21.78 or later, and WhatsApp for Mac to v2.25.21.78 or later. Also apply Apple's backported OS fix for CVE-2025-43300, since the two flaws were combined in the observed attack chain. Review and re-link WhatsApp companion devices if compromise is suspected; federal agencies must follow BOD 22-01 required-action deadlines per the KEV listing.