VulnerabilityPublished 25 Jul 2026Updated 27 Jul 2026

CVE-2026-64456: Linux kernel · hwrng: virtio: clamp device-reported used.len at copy_data()

Source GCVE Database

Authoritative record:CVE-2026-64456· High 7.7

Not known to be exploited · CVSS 7.7 High · fixed in fde19b0d4eeabae042519313c843fe6f27d41e9d : patch Linux kernel soon.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

7.7High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 4% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in fde19b0d4eeabae042519313c843fe6f27d41e9d, e3046eeada299f917a8ad883af4434bfb86556b1, 63335e7b638ae70028ae285bb95153874a8bc852 +5

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H

Attack Vector: Local
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-7vrc-rff8-p548

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < fde19b0d4eeabae042519313c843fe6f27d41e9d	Fixed in fde19b0d4eeabae042519313c843fe6f27d41e9d
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < e3046eeada299f917a8ad883af4434bfb86556b1	Fixed in e3046eeada299f917a8ad883af4434bfb86556b1
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < 63335e7b638ae70028ae285bb95153874a8bc852	Fixed in 63335e7b638ae70028ae285bb95153874a8bc852
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < 285e17c44e3873a73460f294acbd64018ff64385	Fixed in 285e17c44e3873a73460f294acbd64018ff64385
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < 92d5736a62040ec1cfff23ea57e6599301690ad5	Fixed in 92d5736a62040ec1cfff23ea57e6599301690ad5
LinuxLinux	Affected ≥ f7f510ec195781c857ab76366a3e1c59e1caae42, < 81dd21b5f0c299cc7b5bf84f04a61938559d20e6	Fixed in 81dd21b5f0c299cc7b5bf84f04a61938559d20e6

AI-suggested

A fix is available that clamps the device-reported used.len at the point of use and applies array_index_nospec() to prevent out-of-bounds access. Users should apply the official Linux kernel patches that address this issue. Since this is a kernel vulnerability, upgrading to a patched kernel version is the recommended remediation. No additional mitigation is required if the kernel is updated. Patch status is not explicitly confirmed in the provided data; check the vendor advisory for current remediation guidance.

Description

In the Linux kernel, the following vulnerability has been resolved: hwrng: virtio: clamp device-reported used.len at copy_data() random_recv_done() stores the device-reported used.len directly into vi->data_avail. copy_data() then indexes vi->data[] using vi->data_idx (advanced by previous copy_data() calls) and issues a memcpy() without re-validating either value against the posted buffer size sizeof(vi->data) (SMP_CACHE_BYTES bytes, typically 32 or 64). A malicious or buggy virtio-rng backend can set used.len beyond sizeof(vi->data), steering the memcpy() past the end of the inline array into adjacent kmalloc-1k slab bytes. hwrng_fillfn() mixes those bytes into the guest RNG, and guest root can also observe them directly via /dev/hwrng. Concrete impact is inside the guest: - Memory-safety / hardening: any virtio-rng backend that over-reports used.len causes the driver to read past vi->data into unrelated slab contents. hwrng_fillfn() is a kernel thread that runs as soon as the device is probed; no guest userspace interaction is required to first-trigger the OOB. - Cross-boundary leak (confidential-compute threat model): a malicious hypervisor cooperating with a malicious or compromised guest root userspace can use /dev/hwrng as a leak channel for guest-kernel heap data. The host sets a large used.len, guest root reads /dev/hwrng, and the returned bytes contain guest kernel slab contents that were adjacent to vi->data. In practice, confidential-compute guests (SEV-SNP, TDX) usually disable virtio-rng entirely, so this path is narrow, but the fix is still worth carrying because the underlying memory-safety bug contaminates the guest RNG on any host. KASAN confirms the OOB on a 7.1-rc4 guest whose virtio-rng backend has been patched to report used.len = 0x10000: BUG: KASAN: slab-out-of-bounds in virtio_read+0x394/0x5d0 Read of size 64 at addr ffff88800ae0ba20 by task hwrng/52 Call Trace: __asan_memcpy+0x23/0x60 virtio_read+0x394/0x5d0 hwrng_fillfn+0xb2/0x470 kthread+0x2cc/0x3a0 Allocated by task 1: probe_common+0xa5/0x660 virtio_dev_probe+0x549/0xbc0 The buggy address belongs to the object at ffff88800ae0b800 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 0 bytes to the right of allocated 544-byte region [ffff88800ae0b800, ffff88800ae0ba20) Same class of bug as commit c04db81cd028 ("net/9p: Fix buffer overflow in USB transport layer"), which hardened usb9pfs_rx_complete() against unchecked device-reported length in the USB 9p transport. With the clamp at point of use and array_index_nospec() in place, the same harness boots cleanly: copy_data() returns zero for the bogus report, the device-supplied bytes after data_idx are discarded, and the driver issues a fresh request.

Impact

The vulnerability allows a malicious or buggy virtio-rng backend to cause an out-of-bounds read of guest kernel memory, contaminating the guest's random number generator output with adjacent slab data. In confidential compute scenarios, a malicious hypervisor combined with compromised guest root can use this to leak guest kernel heap contents. The issue compromises memory safety and can lead to information disclosure within the guest. However, many confidential compute guests disable virtio-rng, limiting the attack surface. No known exploits are reported in the wild.

Summary

The Linux kernel's virtio-rng driver stored the device-reported used.len value directly without validating it against the buffer size, leading to an out-of-bounds read in copy_data(). A malicious or buggy virtio-rng backend could set used.len beyond the size of the internal data buffer, causing memcpy() to read past the buffer into adjacent kmalloc slab memory. This memory is then mixed into the guest RNG output and can be directly read by guest root via /dev/hwrng. This creates a memory safety issue and a potential cross-boundary information leak in confidential compute environments. The vulnerability was confirmed by KASAN testing and fixed by clamping the used.len value and adding array_index_nospec() to prevent speculative out-of-bounds access.

CWE-125Out-of-bounds Read (opens in a new tab)
Base weaknessCWE Top 25 (2025): #8
The product reads data past the end, or before the beginning, of the intended buffer.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design · Language Selection
Use a language that provides appropriate memory abstractions.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Overread Buffers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Jul 2026, 23:20 UTC

WeaknessesCWE-125

Technical details

References

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