October 2023 Patch Tuesday forecast: Operating system updates and zero-days aplenty

Apple patched an input validation flaw (CVE-2023-41061, CWE-20) in the Wallet component of iOS, iPadOS, and watchOS that can allow arbitrary code execution when a user interacts with a maliciously crafted attachment. The attack is local and requires user interaction (CVSS 7.8, AV:L/UI:R), so the victim must open or act on the crafted attachment — typically delivered through messaging or another application — for the exploit to succeed. A successful attack yields code execution on the device, and media reports describe it as having been used in 'extremely sophisticated attacks' chained with other Apple zero-days. Anyone running iPhone OS (iOS), iPadOS, or watchOS versions prior to iOS/iPadOS 16.6.1 and watchOS 9.6.2 is affected, a population on the order of a billion active devices. Apple disclosed the issue as actively exploited, and CISA added it to the Known Exploited Vulnerabilities (KEV) catalog on 2023-09-11.

Do: Immediately update iPhones and iPads to iOS/iPadOS 16.6.1 or later, and Apple Watch to watchOS 9.6.2 or later. Because the flaw is listed in CISA's KEV catalog and was actively exploited at disclosure, treat patching as urgent for all user fleets, especially high-value targets; until patched, exercise caution with attachments from untrusted sources. No public proof-of-concept is known, but defenders should check fleet OS versions for stragglers on pre-16.6.1 builds.

CVE-2023-41064 is a buffer overflow (CWE-120) in the ImageIO component of Apple iOS, iPadOS, and macOS that is triggered when the system processes a maliciously crafted image. Because ImageIO performs image decoding for messaging and web content, an attacker can reach the flaw through attachments or web pages, and successful exploitation may allow arbitrary code execution on the device. The flaw was exploited in the wild as part of a chain with CVE-2023-41061 (WebKit), which public reporting described as a zero-click, spyware-grade compromise chain used against civil-society targets. All users of iPhones, iPads, and Macs running builds released before Apple's September 2023 fixes are affected, making the exposed population extremely large. The vulnerability was added to the CISA KEV catalog on 2023-09-11, carries a high EPSS score of 45.1% (99th percentile), and no standalone public proof-of-concept is known because exploitation is occurring in real-world attacks rather than labs.

Do: Apply Apple's September 2023 fixes — iOS and iPadOS 16.6.1 or later and macOS Ventura 13.5.2 or later — across all iPhone, iPad, and Mac fleets, which satisfies the CISA KEV required action. Because the observed in-the-wild chain paired this ImageIO bug with the CVE-2023-41061 WebKit flaw, treat unpatched devices as actively targeted and prioritize high-value users and privileged endpoints. If updates cannot be deployed promptly, follow the KEV guidance to apply vendor mitigations or discontinue use of the affected devices.

Apple's WebKit engine, which renders web content for Safari and for essentially all HTML processing on iOS, iPadOS, and macOS, contains a flaw that leads to code execution when processing maliciously crafted web content. It is triggered when a user's browser or embedded web view loads attacker-controlled web content, so simply visiting a hostile page can be enough. Successful exploitation could allow arbitrary code execution within the affected application's context, a common stepping stone to broader device compromise. All users of Apple iOS, iPadOS, macOS, and Safari are potentially affected, as are users of non-Apple products that rely on WebKit for HTML processing. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2023-09-25, indicating confirmed in-the-wild exploitation; no public proof-of-concept is known.

Do: Apply Apple's latest security updates for iOS, iPadOS, macOS, and Safari that patch WebKit, following the vendor instructions referenced by the CISA KEV entry, and treat unpatched WebKit builds as actively exploited. Until systems are patched, restrict exposure to untrusted web content (e.g., limit browsing and in-app web views to trusted sites for high-risk users). Also inventory any non-Apple applications or HTML-processing components in your environment that bundle WebKit and update them as their maintainers ship fixes.

CVE-2023-4863 is a heap-based buffer overflow (CWE-787) in the WebP image codec used by Google Chromium, allowing a remote attacker to write outside the intended bounds of allocated memory. It is triggered when a user visits a crafted HTML page containing malicious WebP image data, so no authentication or special privileges are required, only that the victim loads attacker-controlled content in an affected application. Successful exploitation gives the attacker an out-of-bounds memory write in the affected process, which can lead to application crashes or memory corruption with the potential for code execution. Exposure is unusually broad because, per the advisory, the flaw can affect any application that uses the WebP codec, meaning the browsing public and any software bundling WebP decoding are plausibly in scope. The flaw was added to the CISA KEV catalog on 2023-09-13, indicating confirmed exploitation in the wild; EPSS assigns it a 100% probability of exploitation within 30 days, ransomware use is unknown, and no public proof-of-concept is known.

Do: Update Google Chrome and all other Chromium-based browsers to the latest stable release containing the WebP fix (the patched Chrome 116.0.5845.187 shipped in September 2023), and update or rebuild any other software that bundles the WebP/libwebp codec (fixed in libwebp 1.3.2). Until patching is complete, treat untrusted web content as the attack vector and, per the CISA KEV required action, apply mitigations per vendor instructions or discontinue use of affected software if mitigations are unavailable. Verify remediation by checking installed browser and application versions against the vendor advisories.

The WP Font Awesome plugin for WordPress is vulnerable to Stored Cross-Site Scripting via shortcodes in versions up to, and including, 1.7.9 due to insufficient input sanitization and output escaping on 'icon' user supplied attribute. This makes it possible for authenticated attackers with contributor-level and above permissions to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

CVE-2023-5217 is a heap buffer overflow (CWE-787) in the VP8 encoding path of libvpx, the open-source video codec library bundled with Google's Chromium/Chrome browser. A remote attacker can trigger the flaw by luring a user to a crafted HTML page whose web content invokes the vulnerable VP8 encoding code, corrupting the heap and potentially achieving code execution in the affected browser. Anyone running Google Chrome/Chromium — or other browsers and software that embed libvpx, as CISA notes the library's use is 'not limited to Google Chrome' — is affected. Exploitation is confirmed: CISA added the flaw to the Known Exploited Vulnerabilities catalog on 2023-10-02 (ransomware association: unknown), though no public proof-of-concept is available and a CVSS score has not been published; EPSS puts the 30-day exploitation probability at 49% (99th percentile). Defenders should treat this as an actively exploited browser vulnerability requiring prompt patching.

Do: Update Chrome/Chromium to the vendor release that fixes CVE-2023-5217 — Google shipped the fix with its late-September 2023 stable-channel security update, so verify the exact build number in Google's advisory (it is not specified in the source data). Also patch any other products bundling libvpx (other browsers, media/ffmpeg-based tooling) per vendor instructions, and ensure KEV compliance by applying the required mitigations or discontinuing use of affected builds by the CISA deadline.