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CVE-2026-68299
vmxnet3: fix BUG_ON in vmxnet3_get_hdr_len() for Geneve packets
Published 2026-08-10 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-68299 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.6-1 | Update the kernel and reboot. Fixed in 7.1.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
vmxnet3_get_hdr_len() assumes gdesc->rcd.v4/v6/tcp always describe the outer header, but for a Geneve-encapsulated packet the device can set them based on the inner header instead, signalled by the VMXNET3_RCD_HDR_INNER_SHIFT bit in the completion descriptor. Since the function never skips the outer encapsulation, this mismatch triggers: - BUG_ON(hdr.ipv4->protocol != IPPROTO_TCP), because the outer protocol is UDP (Geneve), not TCP. - BUG_ON(hdr.eth->h_proto != ...), when the tunnel's outer and inner IP versions differ (e.g. outer IPv6/inner IPv4 or vice versa). Check VMXNET3_RCD_HDR_INNER_SHIFT up front and bail out, since the function cannot locate the inner header it would need to parse. Also convert the remaining BUG_ON()s in this function to return 0 defensively.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/net/vmxnet3/vmxnet3_drv.c
- What this is
- VMWARE VMXNET3 ETHERNET DRIVERMAINTAINERS section matched on drivers/net/vmxnet3/ · netdev@vger.kernel.org · Supported
- Kernel module
- vmxnet3
Check it on the machine
grep -w CONFIG_VMXNET3 /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w vmxnet3Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormMnot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieMnot built on armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidMnot built on armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- bookworm · linux-6.12Mnot built on armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_VMXNET3
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-10 (2 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.50%, higher than 41.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.2 | 5.10.265 | 2ddf51fcb6dd |
| 4.2 | 5.15.216 | fbab6b73cc08 |
| 4.2 | 6.1.183 | 28e382646417 |
| 4.2 | 6.6.148 | 667b6e52048e |
| 4.2 | 6.12.101 | 28cb5d8d13b4 |
| 4.2 | 6.18.42 | 4fdb0f162ccd |
| 4.2 | 7.1.6 | b28596baf87e |
| 4.2 | 7.2 | 34a71f5361fc |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The bug is triggered purely by a received Geneve-encapsulated packet processed in the vmxnet3 RX completion path (vmxnet3_rq_rx_complete -> vmxnet3_get_hdr_len); any remote host that can deliver such a frame to a VMware guest's vmxnet3 interface reaches the code, with no local access required.
- AC:LAttack complexity, low
- The attacker only needs to send Geneve-encapsulated TCP traffic larger than the MTU to the target; the device then sets rcd.v4/v6/tcp from the inner header and the outer UDP protocol (or an outer/inner IP version mismatch) deterministically hits the BUG_ON, with no race or memory-layout dependency.
- PR:NPrivileges required, none
- Packet reception and header-length estimation occur in the driver's NAPI RX path before any socket, credential, or authentication check, so an entirely unauthenticated remote sender triggers it.
- UI:NUser interaction, none
- The panic happens during normal NAPI RX processing of an incoming packet; no action by any local user or administrator is needed.
- S:UScope, unchanged
- The BUG_ON crashes the kernel that owns the vmxnet3 interface, and impact stays entirely within that kernel's security authority with no crossing into the hypervisor or another domain.
- C:NConfidentiality impact, none
- The header parsing is bounded by the explicit skb_headlen()/maplen checks, so no out-of-bounds read occurs and no kernel memory contents are disclosed to the attacker before the BUG_ON aborts.
- I:NIntegrity impact, none
- No out-of-bounds or attacker-controlled write occurs; the mismatch is caught by the BUG_ON assertion, which halts execution rather than corrupting kernel memory or control flow.
- A:HAvailability impact, high
- Hitting BUG_ON() in softirq/NAPI context oopses and panics the kernel, taking down the entire guest; a remote attacker can repeat it with a single crafted Geneve packet stream for a persistent denial of service.