SB20261001108 - Ubuntu update for linux
Published: October 1, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 3 vulnerabilities.
1) Improper input validation (CVE-ID: CVE-2026-53221)
CWE-ID: CWE-20 - Improper input validation
CVSSv4: 6.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause traffic to be associated with the wrong tunnel.
The vulnerability exists due to improper input validation in vti6_tnl_lookup() when matching IPv6 VTI tunnels during fallback wildcard tunnel searches. A remote attacker can send network traffic that triggers a hash collision and incorrect tunnel selection to cause traffic to be associated with the wrong tunnel.
The issue occurs because candidate tunnels in the fallback search were not verified to actually use wildcard local or remote addresses.
2) Improper input validation (CVE-ID: CVE-2026-53131)
CWE-ID: CWE-20 - Improper input validation
CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to improper input validation in netfilter Ethernet header handling when processing packets that reach ip6t_eui64, xt_mac, ipset bitmap:ip,mac, hash:ip,mac, hash:mac, or nf_log_syslog code paths without a valid Ethernet MAC header. A remote attacker can send a specially crafted packet to cause a denial of service.
The issue occurs because these paths access eth_hdr(skb) after insufficient validation that the skb is associated with an Ethernet device and that a full MAC header is present.
3) Use-after-free (CVE-ID: CVE-2025-38724)
CWE-ID: CWE-416 - Use After Free
CVSSv4: 8.5 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a local user to escalate privileges on the system.
The vulnerability exists due to a use-after-free error within the nfsd4_setclientid_confirm() function in fs/nfsd/nfs4state.c. A local user can escalate privileges on the system.
Remediation
Install update from vendor's website.