CVE-2025-21764
Description
A vulnerability was found in the Linux kernel's IPv6 Neighbor Discovery (NDISC) subsystem, which manages network neighbor information. The issue arises from improper synchronization mechanisms when allocating socket buffers (sk_buff) in the ndisc_alloc_skb() function. Specifically, the function can be called without holding the necessary Read-Copy-Update (RCU) or Routing Netlink (RTNL) locks, leading to a potential use-after-free (UAF) condition. This flaw allows an attacker with local access and low privileges to exploit the race condition, potentially causing system instability or crashes.
Statement
Red Hat Product Security has rated this bug as Moderate due to the following:
Difficult to exploit reliably:
- Requires winning a race condition in the kernel.
- No known public PoC or exploitation.
- Might be nondeterministic and hard to control memory reuse.
May not lead to code execution:
- Use After Free doesn’t automatically mean control.
- Many kernel UAFs cause crashes but not privilege escalation or info leaks unless paired with other bugs.
Limited exposure:
- Requires IPv6 to be enabled.
- Possibly depends on attacker having raw socket access or other local privileges.
- Mitigations Like KASLR, SLAB hardening, and SELinux may further reduce practical risk.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | N/A | 7.8 |
| Attack Vector | Local | N/A | Local |
| Attack Complexity | High | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | High |
| Integrity Impact | High | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
cve.org: 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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