Week in review: Patched curl and libcurl vulnerability, 15 free M365 security training modules

Atlassian Confluence Data Center and Server contain a broken access control flaw (CWE-20) in publicly accessible instances that allows unauthenticated remote attackers to create unauthorized Confluence administrator accounts and gain access to the instance; the associated public PoC is titled 'Atlassian Confluence Unauthenticated Remote Code Execution'. The flaw is triggered over the network (CVSS 3.1 9.8, AV:N/AC:L/PR:N/UI:N) against any self-managed Confluence instance reachable from the internet, with no privileges or user interaction required. Attackers who exploit it gain administrator-level control of the Confluence instance, and the public PoC demonstrates this extends to unauthenticated code execution. Only self-managed Confluence Data Center and Server deployments are affected; Atlassian Cloud sites hosted on atlassian.net domains are not vulnerable. Exploitation is confirmed in the wild: CISA added it to the KEV on 2023-10-05 with known ransomware use, EPSS is 99.2%, Atlassian reported a handful of customers were already exploited, and Microsoft warned of nation-state (China-linked) abuse.

Do: Patch all internet-facing Confluence Data Center and Server instances to a fixed release per Atlassian's advisory (specific fixed versions are not listed in this data), or restrict public access/discontinue use per CISA's required action. Audit every affected instance for evidence of compromise, especially unauthorized administrator accounts created through this flaw, and report positive findings to CISA. Treat this as urgent given active exploitation by both nation-state actors and ransomware groups.

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.

This flaw makes curl overflow a heap based buffer in the SOCKS5 proxy handshake. When curl is asked to pass along the host name to the SOCKS5 proxy to allow that to resolve the address instead of it getting done by curl itself, the maximum length that host name can be is 255 bytes. If the host name is detected to be longer, curl switches to local name resolving and instead passes on the resolved address only. Due to this bug, the local variable that means "let the host resolve the name" could get the wrong value during a slow SOCKS5 handshake, and contrary to the intention, copy the too long host name to the target buffer instead of copying just the resolved address there. The target buffer being a heap based buffer, and the host name coming from the URL that curl has been told to operate with.

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.

libcue provides an API for parsing and extracting data from CUE sheets. Versions 2.2.1 and prior are vulnerable to out-of-bounds array access. A user of the GNOME desktop environment can be exploited by downloading a cue sheet from a malicious webpage. Because the file is saved to `~/Downloads`, it is then automatically scanned by tracker-miners. And because it has a .cue filename extension, tracker-miners use libcue to parse the file. The file exploits the vulnerability in libcue to gain code execution. This issue is patched in version 2.3.0.

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.