Historical catalog analysis: CISA added this entry on July 20, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.
What the vulnerability is
CVE-2025-53770 is a deserialization of untrusted data vulnerability (CWE-502) affecting on-premises installations of Microsoft SharePoint Server. This flaw could allow an unauthorized attacker to execute code over a network. Notably, this vulnerability serves as a patch bypass for CVE-2025-49704 and can be chained with CVE-2025-53771 to increase impact.
Exposure and applicability
This vulnerability specifically applies to on-premises deployments of Microsoft SharePoint Server. It is particularly critical for organizations that previously applied fixes for CVE-2025-49704, as those protections are bypassed by this flaw. The risk is heightened for environments running end-of-life (EOL) or end-of-service (EOS) versions, including SharePoint Server 2013 and earlier, which do not receive standard security updates.
Potential breach-prevention strategy
Because the source reports known use of this vulnerability in ransomware campaigns, we analyze how similar compromises could be mitigated. The reported entry path is network-based remote code execution via deserialization; however, the specific delivery mechanism for the untrusted data remains unknown.
Prioritized Actions:
1. Isolate EOL/EOS Assets: For SharePoint Server 2013 and earlier, disconnect public-facing instances from the network. This addresses the scenario where unpatchable legacy systems are exposed to the internet. Responsible Role: Network Engineer. Verification: Confirm via firewall logs or external port scans that these assets are no longer reachable from the public web.
2. Update Supported Versions: Apply vendor and CISA-recommended updates for supported versions. This addresses the failure of previous patches (CVE-2025-49704) to prevent this specific exploit path. Responsible Role: Vulnerability Management/System Administrator. Verification: Verify the installation of the specific update associated with CVE-2025-53770.
3. Restrict Network Access: Implement strict access control lists (ACLs) to limit network reachability to SharePoint servers to only authorized users. This is a damage-limiting control intended to reduce the attack surface for unauthorized remote execution. Responsible Role: Security Architect. Verification: Attempt connection from an unauthorized network segment to confirm the request is dropped.
Timing and Limitations: Actions 1 and 2 are primary preventative measures that could have reduced the likelihood of initial compromise if implemented prior to an attack. Action 3 limits exposure but does not fix the underlying flaw. Residual risk remains for any system where patching is delayed or where internal lateral movement occurs after an initial breach.
Remediation priorities
Priority should be given based on asset exposure and support status:
* Immediate: Disconnect public-facing EOL/EOS versions (SharePoint Server 2013 and earlier) as these cannot be patched through standard vendor channels.
* High: Update supported SharePoint Server versions. Organizations that previously patched CVE-2025-49704 must prioritize this update, as the previous fix is insufficient against CVE-2025-53770.
* Critical: Address systems where CVE-2025-53771 may also be present, given the potential for vulnerability chaining.
How to validate remediation
Verification must move beyond simple version checks. To prove exposure was reduced:
* For EOL Assets: Use network mapping or external scanning to provide evidence that public-facing interfaces are disconnected.
* For Supported Assets: Confirm the deployment of the specific update for CVE-2025-53770 and verify through configuration audits that the updated binaries are active in the production environment.
Limits and open questions
It remains unclear if there are viable compensating controls for EOL versions other than total disconnection from public networks. Additionally, while the source notes that updates for CVE-2025-53770 provide more robust protection than those for CVE-2025-49704, it does not specify the exact technical nature of these improvements.
Source and editorial note
CVE-2025-53770: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability · Source date: July 20, 2025 · Retrieved August 31, 2026.
Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.
Archive date: July 23, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: October 08, 2026 at 00:45 UTC.
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