CVE-2026-70264: Defender link-following bug lets a local user read files

What it is

Microsoft Defender has an improper link resolution flaw (CWE-59, “link following”). Defender follows a link, such as a symbolic link or junction, to a file it should not touch. A local attacker with a low-privileged account can use that to read files from the file system. Microsoft’s advisory FAQ describes the impact as “unauthorized file system access - reading from the file system”.

It does not give code execution or let the attacker change or delete files. Microsoft scores it 5.5 (medium) and rates it Important. The attacker must already be on the machine: the vector is local, needs a low-privileged account and no user interaction.

Microsoft lists it as not publicly disclosed and not exploited, with exploitability “Exploitation Less Likely”. The CISA ADP entry in the CVE record also rates exploitation as “none”. The reporter is credited as anonymous. We found no public proof of concept and no report of attacks.

This is a different bug from the 2026 Defender privilege-escalation flaws that were exploited or had public exploit code, such as CVE-2026-33825, CVE-2026-41091 and CVE-2026-69414. Microsoft does not link them.

Am I affected?

You are affected if you run Microsoft Defender (listed as “Windows Defender” in Microsoft’s product tree) at a version before 1.1.26090.9. Microsoft’s advisory says customer action is required.

The 1.1.x numbering matches the Defender Malware Protection Engine version, which Defender normally updates by itself. Machines that block or delay Defender updates, stay offline for long periods, or come from old golden images and VDI templates are the ones most likely to lag.

To check a machine, read the engine version in PowerShell:

Get-MpComputerStatus | Select-Object AMEngineVersion, AMProductVersion

AMEngineVersion and AMProductVersion are properties of the Get-MpComputerStatus output in Microsoft’s documentation. Microsoft’s advisory does not say which of the two version numbers corresponds to 1.1.26090.9; the 1.1.x format points to AMEngineVersion.

What to do

1. Update Defender to 1.1.26090.9 or later. Run Check for updates in Windows Security, or let your normal Defender update channel deliver it.
2. Find machines that are behind in your endpoint management or Defender inventory, starting with shared systems where several people have local accounts.
3. Limit local access on systems that hold sensitive files: remove accounts that do not need to sign in, and keep untrusted users off servers. Microsoft lists no workaround.
4. Do not turn Defender off to avoid the bug unless another endpoint product protects the host.

Because Microsoft reports no exploitation, a hunt is not required. If you want assurance on high-value hosts, use the checks below.

Detection

Microsoft has published no indicators of compromise or detection guidance for this CVE, and we found none from other sources. The flaw only reads files, so a successful attack leaves little behind.

General signs that fit a link-following attack, not tied to this CVE by any source:

• Symbolic links or junctions created by standard users in folders Defender scans, pointing at sensitive locations.
• Unusual file reads by MsMpEng.exe of paths outside normal scan targets.
• Machines with an old AMEngineVersion, which are the only ones exposed.