CVE-2025-53770
CVE-2025-53770 is a security flaw in Microsoft SharePoint, Microsoft’s software for company intranets and shared documents. Attackers can run their own code on Microsoft SharePoint. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 20 Jul 2025, and says ransomware gangs have used it.[1]
Microsoft SharePoint is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 16.0.5513.1001, 16.0.10417.20037 and 16.0.18526.20508.
Description
CISA calls it a deserialization of untrusted data in Microsoft SharePoint. In its words: “Microsoft SharePoint Server on-premises contains a deserialization of untrusted data vulnerability that could allow an unauthorized attacker to execute code over a network. This vulnerability could be chained with CVE-2025-53771. CVE-2025-53770 is a patch bypass for CVE-2025-49704, and the updates for CVE-2025-53770 include more robust protection than those for CVE-2025-49704.”[1]
The CVE record adds: “Deserialization of untrusted data in on-premises Microsoft SharePoint Server allows an unauthorized attacker to execute code over a network. Microsoft is aware that an exploit for CVE-2025-53770 exists in the wild. Microsoft is preparing and fully testing a comprehensive update to address this vulnerability. In the meantime, please make sure that the mitigation provided in this CVE documentation is in place so that you are protected from exploitation.”[2]
The underlying weakness is deserialization of untrusted data (CWE-502), in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Microsoft SharePoint Enterprise Server 2016 | 16.0.5513.1001 |
| Microsoft SharePoint Server 2019 | 16.0.10417.20037 |
| Microsoft SharePoint Server Subscription Edition | 16.0.18526.20508 |
Most families won’t have Microsoft SharePoint; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 20 Jul 2025, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 21 Jul 2025 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at over 99%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s required action: “Disconnect public-facing versions of SharePoint Server that have reached their end-of-life (EOL) or end-of-service (EOS) to include SharePoint Server 2013 and earlier versions.”[1]
- Check whether you use it.Microsoft SharePoint is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 16.0.5513.1001, 16.0.10417.20037 and 16.0.18526.20508), or not in use. CISA gave US government agencies until 21 Jul 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at over 99%.[4] |
See also
Other Microsoft SharePoint flaws
- CVE-2026-65660: code injection ·
- CVE-2026-55040: weak authentication ·
- CVE-2026-50522: deserialization of untrusted data ·
- CVE-2026-58644: deserialization of untrusted data ·
- CVE-2026-20963: deserialization of untrusted data ·
- CVE-2025-49706: improper authentication ·
Other Microsoft flaws
- CVE-2026-96951, Microsoft Windows: command injection ·
- CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
- CVE-2026-81963, Microsoft Windows: link following ·
- CVE-2019-1068, Microsoft SQL Server: remote code execution ·
- CVE-2026-33824, Microsoft Internet Key Exchange (IKE) Service Extensions: double free ·
Other deserialization of untrusted data flaws
- CVE-2021-23758, Ajax.NET Professional: deserialization of untrusted data ·
- CVE-2026-63077, JetBrains TeamCity: deserialization of untrusted data ·
- CVE-2026-45247, Mirasvit Full Page Cache Warmer: full page cache warmer deserialization of untrusted data ·
- CVE-2026-20131, Cisco Secure Firewall Management Center (FMC): software and cisco security cloud control (SCC) firewall management deserialization of untrusted data ·
- CVE-2025-26399, SolarWinds Web Help Desk: deserialization of untrusted data ·
Every Microsoft flaw on CISA’s list · Everything added in July 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft SharePoint Deserialization of Untrusted Data Vulnerability”. Known Exploited Vulnerabilities Catalog, added 20 Jul 2025.
- ^ National Institute of Standards and Technology. “CVE-2025-53770 Detail”. National Vulnerability Database, published 20 Jul 2025.
- ^ Microsoft. Advisories and fixes: microsoft.com, msrc.microsoft.com, msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 1.000, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2025-53770”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.