Out-of-bounds read in Linux kernel Xen sysfs buildid handling
CVE-2026-31786 (XSA-485) is a Linux kernel vulnerability in drivers/xen/sys-hypervisor.c affecting the sysfs exposure of the Xen build ID via /sys/hypervisor/properties/buildid. The Xen hypervisor returns the build ID as binary data that is neither NUL-terminated nor a string. The vulnerable kernel code used sprintf() in buildid_show to copy this value into the sysfs output buffer, causing the kernel to continue reading memory until a zero byte is encountered. This results in an out-of-bounds read from kernel memory. The fix replaces sprintf() with memcpy() so the exact binary length is copied without string interpretation. Supporting advisory text also notes that, in rare cases where no zero byte is encountered within the following sysfs buffer region, the bug may also lead to a write past the 4 KB sysfs buffer.
Are you exposed to this one?
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
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
10 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Linux kernel out-of-bounds read in a Xen-related sysfs file that may leak sensitive information.
A Linux kernel out-of-bounds read in a Xen-related sysfs file that may leak sensitive information.
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.