CVE-2026-74581
Description
A use-after-free vulnerability was found in the Linux kernel's IPv6 FIB rule lookup path. In fib6_rule_suppress(), when a route is suppressed and released via ip6_rt_put_flags(), the res->rt6 pointer is not cleared. If no later rule supplies a replacement route, fib6_rule_lookup() returns the stale (freed) rt6_info to its caller. The subsequent dst_release() then operates on freed memory, hitting rcuref_put_slowpath(). A local attacker who can configure IPv6 routing/FIB rules could trigger this to cause a denial of service (kernel crash) or potentially escalate privileges.
Mitigation
To mitigate this issue, prevent the `ipv6` kernel module from loading. Create a file named `/etc/modprobe.d/disable-ipv6.conf` with the following content:
install ipv6 /bin/true
blacklist ipv6
After creating the file, regenerate the initramfs and reboot the system for the change to take effect. Applications or services that rely on the IPv6 protocol cannot use this mitigation and should prioritize applying the fix.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.8 | N/A | N/A |
| Attack Vector | Local | N/A | N/A |
| Attack Complexity | Low | N/A | N/A |
| Privileges Required | Low | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | High | N/A | N/A |
| Integrity Impact | High | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
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