CVE-2025-21922
Description
From CVE.org
In the Linux kernel, the following vulnerability has been resolved: ppp: Fix KMSAN uninit-value warning with bpf Syzbot caught an "KMSAN: uninit-value" warning [1], which is caused by the ppp driver not initializing a 2-byte header when using socket filter. The following code can generate a PPP filter BPF program: ''' struct bpf_program fp; pcap_t *handle; handle = pcap_open_dead(DLT_PPP_PPPD, 65535); pcap_compile(handle, &fp, "ip and outbound", 0, 0); bpf_dump(&fp, 1); ''' Its output is: ''' (000) ldh [2] (001) jeq #0x21 jt 2 jf 5 (002) ldb [0] (003) jeq #0x1 jt 4 jf 5 (004) ret #65535 (005) ret #0 ''' Wen can find similar code at the following link: https://github.com/ppp-project/ppp/blob/master/pppd/options.c#L1680 The maintainer of this code repository is also the original maintainer of the ppp driver. As you can see the BPF program skips 2 bytes of data and then reads the 'Protocol' field to determine if it's an IP packet. Then it read the first byte of the first 2 bytes to determine the direction. The issue is that only the first byte indicating direction is initialized in current ppp driver code while the second byte is not initialized. For normal BPF programs generated by libpcap, uninitialized data won't be used, so it's not a problem. However, for carefully crafted BPF programs, such as those generated by syzkaller [2], which start reading from offset 0, the uninitialized data will be used and caught by KMSAN. [1] https://syzkaller.appspot.com/bug?extid=853242d9c9917165d791 [2] https://syzkaller.appspot.com/text?tag=ReproC&x=11994913980000
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 | 4.4 | 5.5 | 5.5 |
| Attack Vector | Local | Local | Local |
| Attack Complexity | Low | Low | Low |
| Privileges Required | High | Low | Low |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | None | None | None |
| Integrity Impact | None | None | None |
| Availability Impact | High | High | High |
Vector
Red Hat: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Memory; Read Application Data
When reusing a resource such as memory or a program variable, the original contents of that resource may not be cleared before it is sent to an untrusted party.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
The uninitialized resource may contain values that cause program flow to change in ways that the programmer did not intend.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
