CVE-2025-21922: Linux kernel · ppp: Fix KMSAN uninit-value warning with bpf
Source GCVE Database
Not known to be exploited · CVSS 5.5 Medium.
Data as of 29 Oct 2026, 22:52 UTC
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 1 Apr 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
Description
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
References
- nvd.nist.gov/vuln/detail/CVE-2025-21922 (opens in a new tab)
- git.kernel.org/stable/c/1eacd47636a9de5bee25d9d5962dc538a82d9f0b (opens in a new tab)
- git.kernel.org/stable/c/2f591cb158807bdcf424f66f1fbfa6e4e50f3757 (opens in a new tab)
- git.kernel.org/stable/c/3de809a768464528762757e433cd50de35bcb3c1 (opens in a new tab)
- git.kernel.org/stable/c/4c2d14c40a68678d885eab4008a0129646805bae (opens in a new tab)
- git.kernel.org/stable/c/4e2191b0fd0c064d37b0db67396216f2d4787e0f (opens in a new tab)
- git.kernel.org/stable/c/8aa8a40c766b3945b40565a70349d5581458ff63 (opens in a new tab)
- git.kernel.org/stable/c/c036f5f2680cbdabdbbace86baee3c83721634d6 (opens in a new tab)
- git.kernel.org/stable/c/d685096c8129c9a92689975193e268945fd21dbf (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00030.html (opens in a new tab)
- lists.debian.org/debian-lts-announce/2025/05/msg00045.html (opens in a new tab)