New Microsoft Exchange exploit chain lets ransomware attackers in (CVE-2022-41080)
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2022-41040 +1 in the same advisory: …41082 | Server-Side Request Forgery in Microsoft Exchange Server (ProxyNotShell) 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. | 8.8 group max | 100% | KEV ransomware PoC |
| mass≈250,000+ internet-exposed Exchange servers (public scans of exposed OWA/ECP/Exchange endpoints) | |
| CVE-2022-41080 | Microsoft Exchange Server Privilege Escalation Exploited in Ransomware Campaigns 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. | 8.8 | 77% | KEV ransomware |
| large≈10,000–100,000 internet-exposed on-premises Exchange servers |
Full article415 words · extracted from helpnetsecurity.com · click to collapse
Ransomware-wielding attackers are using a new exploit chain that includes one of the ProxyNotShell vulnerabilities (CVE-2022-41082) to achieve remote code execution on Microsoft Exchange servers. The ProxyNotShell exploit chain used CVE-2022-41040, a SSRF vulnerability in the Autodiscover endpoint of Microsoft Exchange, while this new one uses CVE-2022-41080 to achieve privilege escalation through Outlook Web Access (OWA).
The exploit chain – dubbed OWASSRF by Crowdstrike researchers – can only be headed off by implementing the patches for Microsoft Exchange released in November 2022.
The URL rewrite mitigations for ProxyNotShell that Microsoft shared before the patches were ready are not effective against this exploit method, they say, and urge organizations that cannot apply the patch to temporarily disable OWA.
The clues leading to CVE-2022-41080
The researchers spotted in-the-wild exploitation of CVE-2022-41082 when investigating Play ransomware intrusions where the common entry vector was Microsoft Exchange.
They thought the attackers might have leveraged the ProxyNotShell exploit chain, but found no evidence of exploitation of CVE-2022-41040. Instead, they noticed POST requests made through the OWA endpoint.
The difference between the two exploit chains (Source: Crowdstrike)
In the meantime, Huntress Labs threat researcher Dray Agha managed to grab attack tools via an open repository and among them was a PoC script leveraging an unknown OWA exploit technique and the CVE-2022-41082 exploit.
CrowdStrike researchers successfully deployed the OWASSRF exploit against unpatched Exchange systems, but could not replicate the attack on patched ones. And, since the November KB5019758 patch fixes a DLL hijacking flaw and a flaw whose CVSS score as CVE-2022-41040 and has been marked “exploitation more likely,” they assess “it is highly likely that the OWA technique employed is in fact tied to CVE-2022-41080.”
CVE-2022-41080 is one of the two vulnerabilities four researchers from 360 Noah Lab and VcsLab of Viettel Cyber Security recently concatenated to achieve RCE on Exchange on-premises, Exchange Online and Skype for Business Server. They reported them to Microsoft, who fixed CVE-2022-41080 in November and the other one in December.
“After initial access via this new exploit method, the threat actor leveraged legitimate Plink and AnyDesk executables to maintain access, and performed anti-forensics techniques on the Microsoft Exchange server in an attempt to hide their activity,” Crowdstrike researchers concluded, and provided additional advice for mitigating the risk and detecting signs of exploitation.
UPDATE (December 22, 2022, 06:10 a.m. ET):
Rapid7 has detected an increase in the number of Microsoft Exchange server compromises via this exploit chain, and has provided indicators of compromise related to the campaign.
Text extracted automatically; images, tables and formatting may be missing. Original: https://www.helpnetsecurity.com/2022/12/21/cve-2022-41080/