Windows HTTP.sys Elevation of Privilege Vulnerability
CVE-2026-21240 is a local elevation-of-privilege vulnerability in Windows HTTP.sys caused by a time-of-check time-of-use (TOCTOU) race condition. The flaw affects the Windows kernel HTTP protocol stack component and allows an authorized local attacker to exploit a race between validation and subsequent use of a resource or state within HTTP.sys. The provided content identifies the issue specifically as a TOCTOU race condition in Windows HTTP.sys and classifies it as an elevation-of-privilege vulnerability.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
7 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A privilege escalation vulnerability affecting Windows HTTP.sys.
An elevation of privilege vulnerability in Windows HTTP.sys (no additional details provided in the content).
An elevation of privilege vulnerability in Windows HTTP.sys.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.