Microsoft Patch Tuesday updates for October 2023 fixed three actively exploited zero

CVE-2023-36563 is an information disclosure flaw (CWE-20, improper input validation) in Microsoft WordPad, the lightweight word processor bundled with supported Windows releases; Microsoft has published limited technical detail and CISA describes the flaw as unspecified. An attacker triggers it by persuading a user to open a specially crafted document in WordPad, where improper handling of the document content (including URL/remote-resource references) causes information to be disclosed to the attacker. A successful attacker gains access to sensitive information from the affected system rather than code execution, and exploitation requires user interaction with a malicious file. Any Windows installation with WordPad is potentially affected, making the population essentially the entire supported Windows installed base. Exploitation is confirmed: CISA added the flaw to its KEV catalog on 2023-10-10 and its advisory notes no public proof-of-concept is known and ransomware use is unknown; EPSS is 20.7% (97th percentile), indicating elevated near-term exploitation likelihood.

Do: Apply Microsoft's October 10, 2023 Windows security updates, which include the WordPad fix, prioritizing systems where users open untrusted documents; until patched, follow Microsoft's mitigation guidance to disable the WordPad URL protocol handler via the published registry change. Note that WordPad has since been removed entirely in Windows 11 24H2, so those systems are no longer exposed; per CISA, any ransomware linkage is unknown.

CVE-2023-41763 is a vulnerability in Microsoft Skype for Business Server that Microsoft classifies as an elevation-of-privilege issue, with the underlying weakness mapped to CWE-918 (server-side request forgery). The CVSS vector (AV:N/AC:L/PR:N/UI:N, scope unchanged) shows it can be triggered remotely by an unauthenticated attacker sending crafted network requests, and the impact is confined to confidentiality, meaning an attacker can potentially obtain limited sensitive information from the affected server. Any organization running on-premises Skype for Business Server is potentially affected; the source data does not specify the affected version ranges. The flaw was patched in Microsoft's October 2023 Patch Tuesday, where it was fixed alongside the actively exploited WordPad zero-day (CVE-2023-36563), and it was added to CISA's Known Exploited Vulnerabilities catalog on October 10, 2023, carrying a 90.4% EPSS probability of exploitation within 30 days.

Do: Apply Microsoft's October 2023 Patch Tuesday security updates for Skype for Business Server immediately; CISA's KEV required action is to apply vendor mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. No public proof-of-concept is known, but exploitation is confirmed in the wild, so prioritize internet-facing deployments and review Skype for Business web-service logs for anomalous requests. Check which Skype for Business Server versions your organization runs against Microsoft's advisory to confirm patch applicability.

CVE-2023-44487 is a flaw in the HTTP/2 protocol's stream handling (CWE-400, uncontrolled resource consumption) in which a client opens a large number of streams and immediately cancels them with RST_STREAM frames, forcing the server to repeatedly allocate and tear down per-stream state. When this 'rapid reset' pattern is driven at high volume from many sources, it exhausts server CPU and memory, producing a distributed denial-of-service; Google, Cloudflare and AWS all reported record-scale attacks using this technique. The only impact is availability (denial of service), not code execution or data exposure, but any system speaking HTTP/2 is in scope, including web servers, load balancers, API gateways and CDN edges, and client-side implementations are also affected in a reverse-direction variant. Because the weakness is in the protocol specification itself (attributed to IETF HTTP/2), virtually every deployment with HTTP/2 enabled is affected until vendors ship mitigations or patches. Exploitation is confirmed in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2023-10-10, and EPSS assigns a 100% probability of exploitation within 30 days.

Do: Apply mitigations per vendor instructions as required by CISA KEV/BOD 22-01 guidance — most major web server, load balancer, and CDN vendors have shipped patches or tuning knobs, so check and update each HTTP/2-facing component in your estate. Where patching is not yet possible, limit the number of concurrent HTTP/2 streams per connection, rate-limit new stream creation and inbound HTTP/2 connections, or disable HTTP/2 on internet-exposed servers. Confirm with your CDN or cloud provider that rapid-reset DDoS mitigations are in place at the edge.