The CVSS-EPSS gap in CVE-2026-62815 is the most analytically significant feature of this record. A 9.8 severity score paired with an EPSS of 0.00936 tells you this is a remote code execution vulnerability that lives in a low-probability exploitation band — and that mismatch is intentional signal, not a scoring failure. The use-after-free occurs in Microsoft's QUIC implementation (msquic.dll) and is timing-dependent and heap-context-sensitive, requiring specific connection states, memory layout conditions, and often crafted packet sequences to trigger. That exploitation complexity is precisely why the EPSS remains low. The vulnerability likely surfaced from Microsoft's own fuzzing and security work rather than in-the-wild discovery, which suggests the attack surface is more constrained than the CVSS implies — but also that more similar UAFs may be in their remediation queue. The QUIC protocol's demands on developers — handling connection states, stream states, and frame processing simultaneously across multiple exit points — create the cognitive load where object lifetime mistakes cluster. This isn't negligence; it's the implementation burden of a complex protocol in user space. Watch for whether Microsoft's QUIC patches follow a pattern indicating systematic addressing of this vulnerability class. The immediate action is to verify whether your deployments use msquic.dll in configurations where QUIC connection handling is active (server, client, or both — the specific component matters), apply the Microsoft patch promptly despite the low EPSS, and recognize that the gap paradoxically creates remediation debt: organizations rationally deprioritizing based on EPSS leave themselves exposed during the window before attention shifts elsewhere. The gap reflects today's conditions, not the asymptotic state — as QUIC adoption expands into Azure, Windows Server, and third-party stacks, the reach of this constrained blast radius grows.
CVE-2026-62815
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedUse after free in Microsoft QUIC allows an unauthorized attacker to execute code over a network.
In the news
Third-party coverage- Microsoft patches 400+ vulnerabilities, one zero-day under ...
- Microsoft Patches 398 Flaws Including a Windows Driver Zero-Day Under ...
- Microsoft August 2026 Patch Tuesday fixes 400 flaws, 3 zero-days
- Microsoft Patch Tuesday for August 2026 Fixed a Zero-Day and ...
- August 2026 Patch Tuesday: Microsoft Fixes 421 CVEs, One Exploited ...
Surfaced from public web coverage — external links open in a new tab.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysisMemory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.
General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 10.0.22631.7517< 10.0.26100.9106< 10.0.26200.9106< 10.0.28000.2704< 10.0.20348.5440< 10.0.26100.33222CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data10.0.20348.544010.0.22631.751710.0.26100.9106
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-62815 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesThe CVSS-EPSS gap in CVE-2026-62815 is the most analytically significant feature of this record. A 9.8 severity score paired with an EPSS of 0.00936 tells you this is a remote code execution vulnerability that lives in a low-probability exploitation band — and that mismatch is intentional signal, not a scoring failure. The use-after-free occurs in Microsoft's QUIC implementation (msquic.dll) and is timing-dependent and heap-context-sensitive, requiring specific connection states, memory layout conditions, and often crafted packet sequences to trigger. That exploitation complexity is precisely why the EPSS remains low. The vulnerability likely surfaced from Microsoft's own fuzzing and security work rather than in-the-wild discovery, which suggests the attack surface is more constrained than the CVSS implies — but also that more similar UAFs may be in their remediation queue. The QUIC protocol's demands on developers — handling connection states, stream states, and frame processing simultaneously across multiple exit points — create the cognitive load where object lifetime mistakes cluster. This isn't negligence; it's the implementation burden of a complex protocol in user space. Watch for whether Microsoft's QUIC patches follow a pattern indicating systematic addressing of this vulnerability class. The immediate action is to verify whether your deployments use msquic.dll in configurations where QUIC connection handling is active (server, client, or both — the specific component matters), apply the Microsoft patch promptly despite the low EPSS, and recognize that the gap paradoxically creates remediation debt: organizations rationally deprioritizing based on EPSS leave themselves exposed during the window before attention shifts elsewhere. The gap reflects today's conditions, not the asymptotic state — as QUIC adoption expands into Azure, Windows Server, and third-party stacks, the reach of this constrained blast radius grows.
Practitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-62815 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data