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Linux KVM/x86 'Januscape' shadow-MMU use-after-free, guest-to-host VM escape on Intel and AMD (public PoC host-DoS; RCE withheld); fixed 6.1.177/6.6.144/6.12.95/6.18.38/7.1.3

cve · CVE-2026-53359

Coverage
1
first 2026-07-09 → last 2026-08-08
Latest activity
2026-08-08
Januscape (CVE-2026-53359): 16-year-old KVM shadow-MMU UAF gives a guest root a host escape on both Intel and…
Peak priority
high
1 high
Targets
technology
sectors: technology, public-sector, finance · regions: europe
Sources cited
5
4 hosts

Action items (4)

Do-now tasks recorded on the entries about CVE-2026-53359, newest first. Check the date before acting on an older one.

  • Patch KVM host kernels so they carry upstream commit 81ccda30b4e8 (2026-06-16), confirm your distro's stable kernel includes the backport; this is a host-kernel fix with no guest-side workaround or config toggle.
    2026-07-09CVE-2026-53359 +1
  • On multi-tenant KVM estates, treat any unexplained host kernel panic/reboot that co-occurs with a single tenant's VM activity as a possible exploitation signal and preserve the host for forensics.
    2026-07-09CVE-2026-53359 +1
  • Patch KVM host kernels so they carry both fixes (Januscape commit 81ccda30b4e8 and Zapscape commit 2abd5287f083); there is no guest-side mitigation for either, so a patched guest on an unpatched host is still exposed.
    2026-07-09CVE-2026-53359 +1
  • Turn nested virtualization off for every tenant and workload that does not explicitly need it; where it must stay on for Intel guests, restrict exposure of EPT page-walk lengths 4 and 5 to L1, which is Zapscape's stated precondition.
    2026-07-09CVE-2026-53359 +1

Defender insights

What each entry about CVE-2026-53359 tells a defender to do, newest first.

2026-07-09HIGHJanuscape (CVE-2026-53359): 16-year-old KVM shadow-MMU UAF gives a guest root a host escape on both Intel and AMD

Latest update

Story timeline

  1. 2026-07-09CVE-2026-53359, Linux KVM/x86 "Januscape": shadow-MMU use-after-free enables guest-to-host VM escape on Intel and AMD
    trending-vulnerabilitiesJanuscape (CVE-2026-53359): 16-year-old KVM shadow-MMU UAF gives a guest root a host escape on both Intel and AMD

Hunting pivots

Affected products
Linux Kernel (KVM/x86)
Tags
cloudlpepatch-availablepoc-publicpriv-escvulnerabilities
ATT&CK techniques (2 across 1 tactic)

2 techniques observed across 1 entry about this entity, derived from entry metadata and body evidence, never asserted without a published entry behind it · pinned to MITRE ATT&CK v19.2 · compare on the matrix · Navigator layer (JSON)

  • Privilege EscalationExploitation for Privilege Escalation · Escape to Host

Privilege Escalation TA0004

T1068Exploitation for Privilege Escalation×1

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges. Exploitation of a software vulnerability occurs when an adversary takes advantage of a programming error in a program, service, or within the operating system software or kernel itself to execute adversary-controlled code. Security constructs such as permission levels will often hinder access to information and use of certain techniques, so adversaries will likely need to perform privilege escalation to include use of software exploitation to circumvent those restrictions.

Evidence: 2026-07-09/cve-2026-53359-januscape-kvm-x86-guest-to-host-vm-escape · ATT&CK page ↗

T1611Escape to Host×1

Adversaries may break out of a container or virtualized environment to gain access to the underlying host. This can allow an adversary access to other containerized or virtualized resources from the host level or to the host itself. In principle, containerized / virtualized resources should provide a clear separation of application functionality and be isolated from the host environment.

Evidence: 2026-07-09/cve-2026-53359-januscape-kvm-x86-guest-to-host-vm-escape · ATT&CK page ↗

Entries about Linux KVM/x86 'Januscape' shadow-MMU use-after-free, guest-to-host VM escape on Intel and AMD (public PoC host-DoS; RCE withheld); fixed 6.1.177/6.6.144/6.12.95/6.18.38/7.1.3 (1)

2026-07-09 · view entry permalink →

HIGHCVE-2026-53359 +1updated

CVE-2026-53359, Linux KVM/x86 "Januscape": shadow-MMU use-after-free enables guest-to-host VM escape on Intel and AMD

Researcher Hyunwoo Kim (V4bel) disclosed Januscape (CVE-2026-53359), a use-after-free in the shadow-MMU emulation of KVM/x86 (arch/x86/kvm/mmu/mmu.c) whose root cause traces to a 2010 commit, roughly 16 years dormant before the fix landed upstream on 16 June 2026 (BleepingComputer, 2026-07-07). The bug fires when kvm_mmu_get_child_sp() reuses a shadow page without comparing its role, producing a mismatched direct/indirect flag and an incorrect GFN computation; orphaned rmap entries survive memslot deletion and are later dereferenced after the backing memory is freed (V4bel, 2026-07-07). The upstream fix is commit 81ccda30b4e8 (16 June 2026); the researcher gives the vulnerable range as commit 2032a93d66fa (2010-08-01) through that fix (kernel.org, 2026-06-16; V4bel, 2026-07-07).

This is a genuine guest-to-host escape: a root user inside a KVM guest can trigger the UAF from purely guest-side actions, on both Intel and AMD hosts, the researcher calls it "the first guest-to-host exploit research triggerable on both" vendors (V4bel, 2026-07-07). Januscape was submitted as a live 0-day against Google's kvmCTF program. A public PoC that panics the host kernel (a denial of service against every co-tenant on the same physical host) is released; a full working host-compromise/RCE exploit exists but the researcher is deliberately withholding it (BleepingComputer, 2026-07-07). Mapped to T1611 Escape to Host.

With guest-side actions alone, an attacker can compromise the host that runs their VM. For example, an attacker who has rented just a single instance on a public cloud could panic the host kernel to take down every other tenant VM on the same physical machine (DoS), or run code with root privilege on the host to take over the host and all the guests on it (RCE).

BleepingComputer 2026-07-07

This is the first guest-to-host exploit research triggerable on both Intel and AMD

Hyunwoo Kim (V4bel), researcher write-up + PoC 2026-07-07

These two vulnerabilities can let an attacker run commands on the host by escaping the guest virtual machine, this can lead to a full system compromise since the attacker can escape the virtual environment.

This vulnerability can only be exploited by attackers with root privileges and systems with Intel architecture need both EPT page walk length 4 and 5 exposed to L1.

Distributions like RHEL can allow an unprivileged user to gain root privileges.

Centre for Cybersecurity Belgium (CCB) 2026-08-07

can be triggered on Intel without any particular constraint as long as nested virtualization is enabled, but Zapscape requires that both EPT page walk length 4 and 5 be exposed to L1 on Intel. On AMD there is no such constraint.

V4bel, researcher write-up 2026-08-06
Updaterun 2026-08-08T0409Z-intelactionsaffected_productscvesevidenceregionssourcestagstechniquesbody

Januscape has a sibling. Zapscape (CVE-2026-64561) was assigned on 2026-08-04 and is a use-after-free in the same KVM/x86 shadow MMU, but in a different path: where Januscape came from shadow-page role confusion, Zapscape fires when a guest using nested virtualization makes KVM recursively zap a root shadow page that is still in use during MMU page-quota reclaim, leaving KVM handling a fault on a root that has already been invalidated (V4bel, 2026-08-06). The upstream fix, commit 2abd5287f083, moves the stale-root check after make_mmu_pages_available() (V4bel, 2026-08-06).

Belgium's Centre for Cybersecurity turned the pair into a single operational instruction on 2026-08-07, publishing a "Patch Immediately" advisory that treats both CVEs together, scores each CVSS 8.8 (AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H), and states that they "can let an attacker run commands on the host by escaping the guest virtual machine, this can lead to a full system compromise since the attacker can escape the virtual environment" (CCB, 2026-08-07).

Two preconditions decide who is actually exposed, and they differ between the two bugs. Januscape "can be triggered on Intel without any particular constraint as long as nested virtualization is enabled, but Zapscape requires that both EPT page walk length 4 and 5 be exposed to L1 on Intel. On AMD there is no such constraint" (V4bel, 2026-08-06); CCB states Zapscape "can only be exploited by attackers with root privileges and systems with Intel architecture need both EPT page walk length 4 and 5 exposed to L1" (CCB, 2026-08-07). The guest-root precondition sounds like a high bar and often is not: CCB adds that "Distributions like RHEL can allow an unprivileged user to gain root privileges," and on rented cloud instances guest root is simply what the tenant has (CCB, 2026-08-07). The researcher's current public demonstration runs on AMD nested SVM/NPT (V4bel, 2026-08-06).

vulnerability09 Jul 04:32Zmulti-sourceOpen finding →
Sources: BleepingComputer · Hyunwoo Kim (V4bel), researcher write-up + PoC · Linux kernel upstream fix commit · Centre for Cybersecurity Belgium (CCB) · V4bel, researcher write-up

Co-occurring entities

Derived: referenced by the same focused operational entries (weekly summaries and report roundups don't count); ×N counts the shared entries.

Where this entity is cited

  • Vulns1

Source distribution

  • github.com2 (40%)
  • bleepingcomputer.com1 (20%)
  • ccb.belgium.be1 (20%)
  • git.kernel.org1 (20%)

External references

NVD · cve.org · CISA KEV

All cited sources (5)