high CVSS 7.8

CVE-2021-47061·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: KVM: Destroy I/O bus devices on unregister failure _after_ sync'ing SRCU If allocating a new instance of an I/O bus fails when unregistering a device, wait to destroy the device until after all readers are guaranteed to see the new null bus. Destroying devices before the bus is nullified could lead to use-after-free since readers expect the devices on their reference of the bus to remain valid.

Severity
high
Software
Kernel
Fixed in
5.12.4
Published
2024-02-29

Affected versions

From: 5.12

Until: 5.12.4

Fixed in: 5.12.4

How to fix this CVE

Update your Linux kernel to version 5.12.4 or later to resolve a critical memory safety issue in KVM's I/O bus device handling. This vulnerability can lead to use-after-free conditions when device unregistration fails, potentially allowing local privilege escalation. Apply the kernel update immediately if you are running an affected 5.12.x kernel on a system with KVM virtualization enabled.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Run 'uname -r' to check your current kernel version. If it shows 5.12.0 through 5.12.3, your system is vulnerable.
  2. Verify KVM is enabled by checking if '/sys/module/kvm' exists and 'lsmod | grep kvm' returns output.
  3. Check dmesg and /var/log/kern.log for error messages containing 'io_bus' or 'kvm' combined with 'allocation' or 'unregister' failures.
  4. After patching, reboot and run 'uname -r' again to confirm the kernel version is 5.12.4 or higher, and verify '/sys/module/kvm' still functions normally.

FAQ

What is CVE-2021-47061?

This is a use-after-free vulnerability in KVM's I/O bus device management where improper cleanup during device unregistration can leave freed device references accessible to active readers, potentially enabling local privilege escalation on systems running the affected kernel versions.

Is CVE-2021-47061 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are currently available.

What versions of Kernel are affected by CVE-2021-47061?

Linux kernel versions 5.12 through 5.12.3 are vulnerable. The issue is resolved in kernel 5.12.4 and all subsequent releases.

How do I check if my server is vulnerable to CVE-2021-47061?

Run 'uname -r' and check if the output shows kernel version 5.12.0, 5.12.1, 5.12.2, or 5.12.3. If it does and KVM is enabled (verify with 'lsmod | grep kvm'), your system requires an immediate kernel update.

Does Defensia detect CVE-2021-47061?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Kernel is installed on a monitored server, CVE-2021-47061 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-52986CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack_sip: don't use simple_strtoul Replace unsafe port parsing in epaddr_len(), ct_sip_parse_header_uri(), and ct_sip_parse_request() with a new sip_parse_port() helper that validates each digit against the buffer limit, eliminating the use of simple_strtoul() which assumes NUL-terminated strings. The previous code dereferenced pointers without bounds checks after sip_parse_addr() and relied on simple_strtoul() on non-NUL-terminated skb data. A port that reaches the buffer limit without a trailing character is also rejected as malformed. Also get rid of all simple_strtoul() usage in conntrack, prefer a stricter version instead. There are intentional changes: - Bail out if number is > UINT_MAX and indicate a failure, same for too long sequences. While we do accept 05535 as port 5535, we will not accept e.g. 'sip:10.0.0.1:005060'. While its syntactically valid under RFC 3261, we should restrict this to not waste cycles when presented with malformed packets with 64k '0' characters. - Force base 10 in ct_sip_parse_numerical_param(). This is used to fetch 'expire=' and 'rports='; both are expected to use base-10. - In nf_nat_sip.c, only accept the parsed value if its within the 1k-64k range. - epaddr_len now returns 0 if the port is invalid, as it already does for invalid ip addresses. This is intentional. nf_conntrack_sip performs lots of guesswork to find the right parts of the message to parse. Being stricter could break existing setups. Connection tracking helpers are designed to allow traffic to pass, not to block it. Based on an earlier patch from Jenny Guanni Qu <qguanni@gmail.com>.
CVE-2026-63993CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu() skb_tunnel_check_pmtu() can change skb->head. Reusing old_iph afer skb_tunnel_check_pmtu() can cause an UAF. Use instead ip_hdr(skb) as done in drivers/net/bareudp.c and drivers/net/geneve.c. Found by Sashiko.
CVE-2026-64046CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: tls: prevent chain-after-chain in plain text SG Sashiko points out that if end = 0 (start != 0) the current code will create a chain link to content type right after the wrap link: This would create a chain where the wrap link points directly to another chain link. The scatterlist API sg_next iterator does not recursively resolve consecutive chain links. meaning this is illegal input to crypto. The wrapping link is unnecessary if end = 0. end is the entry after the last one used so end = 0 means there's nothing pushed after the wrap: end start i v v v [ ]...[ ][ d ][ d ][ d ][ d ][rsv for wrap] Skip the wrapping in this case. TLS 1.3 can use the "wrapping slot" for it's chaining if end = 0. This avoids the chain-after-chain. Move the wrap chaining before marking END and chaining off content type, that feels like more logical ordering to me, but should not matter from functional perspective.
CVE-2026-64055CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: net: ethernet: cortina: Carry over frag counter The gmac_rx() NAPI poll function assembles packets in an SKB from a ring buffer. If the ring buffer gets completely emptied during a poll cycle, we exit gmac_rx(), but the packet is not yet completely assembled in the SKB, yet the fragment counter frag_nr is reset to zero on the next invocation. Solve this by making the RX fragment counter a part of the port struct, and carry it over between invocations. Reset the fragment counter only right after calling napi_gro_frags(), on error (after calling napi_free_frags()) or if stopping the port. Reset it in some place where not strictly necessary just to emphasize what is going on. This was found by Sashiko during normal patch review.

References

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