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CVE-2026-64046
net: tls: prevent chain-after-chain in plain text SG
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem net/tls. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-64046 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 | fixed | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Sashiko points out that if end = 0 (start != 0) the current code will create a chain link to content type right after the wrap link: This would create a chain where the wrap link points directly to another chain link. The scatterlist API sg_next iterator does not recursively resolve consecutive chain links. meaning this is illegal input to crypto. The wrapping link is unnecessary if end = 0. end is the entry after the last one used so end = 0 means there's nothing pushed after the wrap: end start i v v v [ ]...[ ][ d ][ d ][ d ][ d ][rsv for wrap] Skip the wrapping in this case. TLS 1.3 can use the "wrapping slot" for it's chaining if end = 0. This avoids the chain-after-chain. Move the wrap chaining before marking END and chaining off content type, that feels like more logical ordering to me, but should not matter from functional perspective.
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.
net/tls/tls_sw.c
- What this is
- NETWORKING [TLS]MAINTAINERS section matched on net/tls/ · netdev@vger.kernel.org · Maintained
- Kernel module
- tls
Check it on the machine
grep -w CONFIG_TLS /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 tlsPrints 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 as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_TLS
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
- 2026-07-19 (3 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.51%, higher than 42.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/tls
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.5 | 5.10.258 | 49a5faaa471d |
| 5.5 | 5.15.209 | 91359966e247 |
| 5.5 | 6.1.175 | 410351158dfe |
| 5.5 | 6.6.142 | acdc12b71c9a |
| 5.5 | 6.12.92 | 929b1548e63a |
| 5.5 | 6.18.34 | af855f4c966a |
| 5.5 | 7.0.11 | b9c015ef1a7b |
| 5.5 | 7.1 | ff26a0e8377d |
| 5.4.14 | 0 | 0 |
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 in kTLS software TX (`tls_push_record` in `net/tls/tls_sw.c`), reached when encrypting outbound TLS 1.3 records on a connected socket; a remote TLS peer triggers this path on internet-facing servers and L7 proxies (kTLS+sockmap) by causing the host to send TLS responses.
- AC:LAttack complexity, low
- The wrapped `sk_msg` ring state (`end=0`, `start!=0`) needed to hit the chain-after-chain bug is deterministically created via BPF `sk_msg` helpers (`bpf_msg_push_data`/`bpf_msg_pop_data`), which the attacker controls on the local path or can steer on servers whose sockmap programs manipulate messages based on connection traffic.
- PR:NPrivileges required, none
- Exploitation does not require Linux capabilities on the attacking side when targeting a TLS service already running kTLS with sockmap; any unauthenticated remote client that completes a TLS 1.3 handshake and causes record transmission can reach the vulnerable encrypt path.
- UI:NUser interaction, none
- No victim user action beyond normal automated TLS server/client operation is required; triggering the bug is achieved through crafted network traffic and/or syscall-driven sends on an already-established kTLS socket.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and privilege escalation within the same host/kernel security boundary, not a cross-boundary escape such as VM guest-to-host or IOMMU bypass.
- C:HConfidentiality impact, high
- Passing a scatterlist with consecutive chain links to `crypto_aead_encrypt` is illegal; the crypto scatterwalk treats chain entries as data pages, causing out-of-bounds kernel memory reads and information disclosure primitives.
- I:HIntegrity impact, high
- The malformed scatterlist fed to AEAD encryption can cause the crypto layer to write ciphertext to incorrect kernel addresses, providing a memory corruption primitive that can be developed into arbitrary kernel write or code execution.
- A:HAvailability impact, high
- Invalid scatterlist traversal in the crypto path can dereference bogus page pointers and kernel-oops the system; encryption failure also invokes `tls_err_abort`, reliably disrupting the affected TLS connection and potentially the hosting service.