Ransomware Hackers Using New Way to Bypass MS Exchange ProxyNotShell Mitigations
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 article532 words · extracted from thehackernews.com · click to collapse
Ravie LakshmananDec 21, 2022Email Security / Data Security
Threat actors affiliated with a ransomware strain known as Play are leveraging a never-before-seen exploit chain that bypasses blocking rules for ProxyNotShell flaws in Microsoft Exchange Server to achieve remote code execution (RCE) through Outlook Web Access (OWA).
"The new exploit method bypasses URL rewrite mitigations for the Autodiscover endpoint," CrowdStrike researchers Brian Pitchford, Erik Iker, and Nicolas Zilio said in a technical write-up published Tuesday.
Play ransomware, which first surfaced in June 2022, has been revealed to adopt many tactics employed by other ransomware families such as Hive and Nokoyawa, the latter of which upgraded to Rust in September 2022.
The cybersecurity company's investigations into several Play ransomware intrusions found that initial access to the target environments was not achieved by directly exploiting CVE-2022-41040, but rather through the OWA endpoint.
Dubbed OWASSRF, the technique likely takes advantage of another critical flaw tracked as CVE-2022-41080 (CVSS score: 8.8) to achieve privilege escalation, followed by abusing CVE-2022-41082 for remote code execution.
It's worth noting that both CVE-2022-41040 and CVE-2022-41080 stem from a case of server-side request forgery (SSRF), which permits an attacker to access unauthorized internal resources, in this case the PowerShell remoting service.
CrowdStrike said the successful initial access enabled the adversary to drop legitimate Plink and AnyDesk executables to maintain persistent access as well as take steps to purge Windows Event Logs on infected servers to conceal the malicious activity.
All three vulnerabilities were addressed by Microsoft as part of its Patch Tuesday updates for November 2022. It's, however, unclear if CVE-2022-41080 was actively exploited as a zero-day alongside CVE-2022-41040 and CVE-2022-41082.
The Windows maker, for its part, has tagged CVE-2022-41080 with an "Exploitation More Likely" assessment, implying it's possible for an attacker to create exploit code that could be utilized to reliably weaponize the flaw.
CrowdStrike further noted that a proof-of-concept (PoC) Python script discovered and leaked by Huntress Labs researcher Dray Agha last week may have been put to use by the Play ransomware actors for initial access.
This is evidenced by the fact that the execution of the Python script made it possible to "replicate the logs generated in recent Play ransomware attacks."
"Organizations should apply the November 8, 2022 patches for Exchange to prevent exploitation since the URL rewrite mitigations for ProxyNotShell are not effective against this exploit method," the researchers said.
Update
Cybersecurity company Rapid7, in a related advisory on Wednesday, said it has observed an "increase in the number of Microsoft Exchange Server compromises" through the aforementioned OWASSRF exploit chain to gain remote code execution.
"Patched servers do not appear vulnerable, servers only utilizing Microsoft's mitigations do appear vulnerable," Rapid7 researcher Glenn Thorpe noted. "Threat actors are using this to deploy ransomware."
In a statement shared with The Hacker News, a Microsoft spokesperson said "the reported method exploits vulnerable systems that have not applied our latest security updates," adding "customers should prioritize installing the latest updates, specifically our November 2022 Exchange Server updates."
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