US CISA adds MS Exchange bug CVE-2022-41080 to its Known Exploited Vulnerabilities Catalog

CVE-2022-41040 is a server-side request forgery (SSRF, CWE-918) vulnerability in Microsoft Exchange Server, publicly tracked under the name "ProxyNotShell" together with CVE-2022-41082. It is triggered when an attacker sends crafted HTTP requests to exposed Exchange web endpoints (such as Autodiscover), causing the server to issue attacker-influenced requests to itself. On its own the SSRF coerces authenticated server-side requests, but when chained with the CVE-2022-41082 remote code execution flaw it gives the attacker code execution on the Exchange server, typically followed by web shells, data access, and — in observed campaigns — ransomware deployment. Organizations running on-premises Microsoft Exchange Server are affected; the source data lists only Microsoft Exchange Server and does not specify affected version ranges, and hosted Exchange Online is a separate product not listed here. The vulnerability is being actively exploited in the wild: it was added to CISA's Known Exploited Vulnerabilities catalog on 2022-09-30 with known ransomware use, and EPSS assigns it a 100% probability of exploitation within 30 days; no public PoC is listed.

Do: Apply Microsoft's Exchange Server security updates per vendor instructions immediately, as required by the CISA KEV catalog. As interim mitigation, restrict or block untrusted internet access to Exchange web endpoints (e.g., Autodiscover, OWA, ECP), and review IIS logs for suspicious crafted requests indicating SSRF or the chained CVE-2022-41082 exploitation. Given documented ransomware use, prioritize any internet-facing Exchange server and hunt for web shells and post-exploitation activity.

CVE-2022-41080 is an elevation-of-privilege flaw in Microsoft Exchange Server that stems from improper handling of requests to the server's Autodiscover component, allowing an attacker with any valid authenticated mailbox account to escalate privileges on the server. It is triggered by sending crafted authenticated HTTP requests to the Autodiscover endpoint, and it lets attackers bypass the URL-rewrite mitigations defenders had deployed against the earlier ProxyNotShell SSRF. When chained with the related PowerShell remote-code-execution bug CVE-2022-41082, privilege escalation becomes full remote code execution on the Exchange server. Any organization running on-premises Exchange Server with the Autodiscover component reachable — especially internet-exposed OWA/Autodiscover endpoints — is affected. The flaw is actively exploited: it was added to CISA's KEV catalog on 2023-01-10, is known to be used by ransomware operators, and has been tied to the Play ransomware gang, including the attack that took Rackspace's hosted Exchange environment offline.

Do: Apply Microsoft Exchange Server security updates per vendor instructions (this CVE was fixed in Microsoft's November 2022 Exchange security updates — verify your servers are fully patched through the January 2023 rollups and that no Exchange builds predate the fix). Until patched, apply and verify the Autodiscover URL-rewrite/allow-list mitigation, knowing this flaw is a known bypass vector, and restrict Autodiscover/OWA exposure where feasible. Hunt for compromise in IIS logs for unusual requests to /autodiscover/autodiscover.json followed by PowerShell (CVE-2022-41082) activity, and treat any suspicious authenticated sessions as potential ransomware precursor activity.

CVE-2023-21674 is a use-after-free flaw (CWE-416) in the Windows Advanced Local Procedure Call (ALPC) facility, the kernel-level mechanism Windows uses for fast communication between processes and system services. An attacker who can already run code on a Windows machine can trigger the bug by sending crafted ALPC requests, corrupting memory in a privileged process. Successful exploitation allows a local, low-privileged attacker to elevate to SYSTEM/administrator privileges, typically to gain full control of the host or to complete an exploit chain after an initial compromise. Essentially all supported Windows client and server installations from Microsoft are affected; the source data does not list specific versions, and the fix shipped with Microsoft's January 2023 Patch Tuesday, which addressed a record 974 vulnerabilities including this and one other actively exploited Windows zero-day. CISA added the CVE to the Known Exploited Vulnerabilities catalog on 2023-01-10, confirming exploitation in the wild; no public proof-of-concept is known, ransomware use is undetermined, and EPSS estimates a 41.8% probability of exploitation in the next 30 days (99th percentile).

Do: Apply Microsoft's January 2023 (released 2023-01-10) or later Windows cumulative security updates to all Windows clients and servers, per CISA's required action to 'apply updates per vendor instructions.' Because this is a local privilege escalation, prioritize hosts where low-privileged users or untrusted code execute, such as endpoints, RDS/VDI servers, and multi-user systems, and verify installation via your update-management inventory. Treat this as actively exploited; with no public PoC or documented workaround, timely patching is the primary mitigation.