CVE-2026-90160
lwt_bpf: Restore reserved headroom after xmit program
Published Sep 17, 2026
CVSS n/a
EPSS < 1%
KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:
lwt_bpf: Restore reserved headroom after xmit program
ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT
xmit. An LWT_XMIT BPF program can then modify the skb head and still
return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the
skb continues to neighbour output.
That recheck uses dst->dev->hard_header_len. This is not enough for the
neighbour cached-header path: neigh_hh_output() copies the cached hardware
header using the aligned hh_cache size, HH_DATA_MOD for short headers or
HH_DATA_ALIGN(hh_len) otherwise.
On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If
an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can
still have 15 bytes of headroom after the program. The existing check
accepts that, after which neigh_hh_output() hits its headroom warning and
drops the skb.
Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match
the reservation made before LWT xmit.
lwt_bpf: Restore reserved headroom after xmit program
ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT
xmit. An LWT_XMIT BPF program can then modify the skb head and still
return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the
skb continues to neighbour output.
That recheck uses dst->dev->hard_header_len. This is not enough for the
neighbour cached-header path: neigh_hh_output() copies the cached hardware
header using the aligned hh_cache size, HH_DATA_MOD for short headers or
HH_DATA_ALIGN(hh_len) otherwise.
On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If
an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can
still have 15 bytes of headroom after the program. The existing check
accepts that, after which neigh_hh_output() hits its headroom warning and
drops the skb.
Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match
the reservation made before LWT xmit.
Affected Products
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CVE record
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NVD configurations
No data
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Red Hat packages
No data
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OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
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| Linux | Linux | affected |
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No data.
No data.
| Vendor | Product | Versions | ||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel |
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| Linux | Linux Kernel |
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Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DLA |
DLA-4817-1 | linux-6.12 security update |
| Debian DLA |
DLA-4841-1 | linux security update |
 Debian DSA |
DSA-6528-1 | linux security update |
 Ubuntu USN |
USN-8961-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9019-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9020-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9022-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9023-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9024-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9025-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9026-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9029-1 | Linux kernel (Raspberry Pi) vulnerabilities |
| Ubuntu USN |
USN-9039-1 | Linux kernel (Azure CVM) vulnerabilities |
| Ubuntu USN |
USN-9040-1 | Linux kernel (Low Latency NVIDIA) vulnerabilities |
| Ubuntu USN |
USN-9066-1 | Linux kernel (HWE) vulnerabilities |
| Ubuntu USN |
USN-9091-1 | Linux kernel (NVIDIA Tegra) vulnerabilities |
Metrics
No CVSS v4.0
No CVSS v3.1
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.216% probability within 30 days)
Key SSVC decision points have not yet been added.
References
History
Sep 20, 2026 2:15 AM
Weaknesses updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-20 |
Sep 17, 2026 4:30 PM
Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: lwt_bpf: Restore reserved headroom after xmit program ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT xmit. An LWT_XMIT BPF program can then modify the skb head and still return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the skb continues to neighbour output. That recheck uses dst->dev->hard_header_len. This is not enough for the neighbour cached-header path: neigh_hh_output() copies the cached hardware header using the aligned hh_cache size, HH_DATA_MOD for short headers or HH_DATA_ALIGN(hh_len) otherwise. On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can still have 15 bytes of headroom after the program. The existing check accepts that, after which neigh_hh_output() hits its headroom warning and drops the skb. Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match the reservation made before LWT xmit. | |
| Title | lwt_bpf: Restore reserved headroom after xmit program | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
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Subscriptions
Weaknesses
