macvlan: inherit needed_headroom and needed_tailroom from lowerdev (CVE-2026-74743) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-74743

macvlan: inherit needed_headroom and needed_tailroom from lowerdev

Answer in brief

CVE-2026-74743 records a Unknown severity vulnerability in macvlan: inherit needed_headroom and needed_tailroom from lowerdev. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 26, 2026Updated Aug 26, 2026Source checked Aug 26, 2026First seen by HOL Aug 26, 2026Material review Aug 26, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <8cd90e850e434577bf6774778657d26d6995e53f \|\| >=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <28afc87bd8da0b3348bbbd834c8a89e83712cf5e \|\| >=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <8f6a05dbac05725e0786701eb04778c5bdbe4eaa \|\| >=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <96fa90b74385b7f2b0d97251dd43d5ee6ca44668 \|\| >=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <bc9a00fb78e32bccc39d763bfd13a450705bac5d \|\| >=b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53 <cef51860becd9700217c81732ca1eb1ea6ed6fe1	8cd90e850e434577bf6774778657d26d6995e53f, 28afc87bd8da0b3348bbbd834c8a89e83712cf5e, 8f6a05dbac05725e0786701eb04778c5bdbe4eaa, 96fa90b74385b7f2b0d97251dd43d5ee6ca44668, bc9a00fb78e32bccc39d763bfd13a450705bac5d, cef51860becd9700217c81732ca1eb1ea6ed6fe1
Linux/Linuxgeneric	2.6.23	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to 8cd90e850e434577bf6774778657d26d6995e53f if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Aug 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 26, 2026

Sources and claim methodology

Upstream source description

In the Linux kernel, the following vulnerability has been resolved: macvlan: inherit needed_headroom and needed_tailroom from lowerdev macvlan devices inherit hard_header_len from lowerdev during macvlan_init(), but leave needed_headroom and needed_tailroom set to 0. When the underlying lowerdev requires extra headroom or tailroom for headers/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx headroom), upper layers calculating packet headroom and tailroom fail to reserve sufficient space. This can result in reallocation overhead, skb headroom underflows, or KASAN slab-use-after-free crashes when dev_hard_header() / macvlan_hard_header() prepends header data or when lower devices append tailroom. Fix this by: 1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init(). 2. Propagating needed_headroom and needed_tailroom updates to attached macvlans in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.

Quoted source text, attributed separately from HOL analysis.