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CVE-2026-74611
tls: rx: restore msg_iter before TLS 1.3 optimistic retry
Published 2026-08-22 (2 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-2026-74611 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
tls_decrypt_sg() advances msg->msg_iter when it maps user pages for the optimistic TLS 1.3 zero-copy path. If the decrypted record turns out not to be unpadded application data, tls_decrypt_sw() retries into a kernel skb, but leaves the iterator advanced. The subsequent copy from the skb then writes decrypted bytes again at a later point in the caller iovecs while recvmsg() reports only the post-retry length. A TLS peer can trigger this after the receiver enables TLS_RX_EXPECT_NO_PAD. Revert the iterator by the number of bytes consumed by the optimistic mapping before retrying without zero-copy. Add a selftest which sends a TLS 1.3 control record with TLS_RX_EXPECT_NO_PAD enabled and verifies that recvmsg() does not overwrite later iovecs beyond the returned length.
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
tools/testing/selftests/net/tls.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
- 2026-08-22 (2 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
- 0.65%, higher than 50.1% 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 |
|---|---|---|
| 6.0 | 6.18.45 | 68787940274e |
| 6.0 | 7.1.9 | 3c837266a734 |
| 6.0 | 7.2 | 1c8629651cb5 |
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 RX (tls_decrypt_sw/tls_sw_recvmsg) and is driven by TLS 1.3 records received from a remote TCP peer; per kernel CNA guidance, kTLS flaws triggered by peer ciphertext on an established connection are Network-reachable (e.g., malicious client to nginx/HAProxy/NVMe-oF-TLS server).
- AC:LAttack complexity, low
- Once the receiver has TLS 1.3 kTLS RX with TLS_RX_EXPECT_NO_PAD, a remote peer can deterministically trigger the optimistic-decrypt retry by sending a non-application-data inner record (handshake/alert/KeyUpdate) or padded data; no race, special heap layout, or rare kernel build is required.
- PR:NPrivileges required, none
- Exploitation requires only being the remote TLS peer on an established kTLS connection; the attacker needs no credentials or Linux capabilities on the victim host. TLS_RX_EXPECT_NO_PAD is a receiver-side performance option set by the service, not an attacker privilege gate.
- UI:NUser interaction, none
- No victim user action beyond normal automated server operation (maintaining a TLS session and calling recvmsg on kTLS sockets). The attacker triggers the flaw solely by sending protocol-valid TLS records over the network.
- S:UScope, unchanged
- The out-of-bounds write corrupts user-space iovec buffers of the process owning the kTLS socket within the same security authority; it does not cross a VM, IOMMU, or sandbox boundary to another security domain.
- C:HConfidentiality impact, high
- skb_copy_datagram_msg writes decrypted peer-controlled bytes past the recvmsg-reported length into adjacent user buffers. This memory corruption can be leveraged for information disclosure via heap/stack grooming even though the immediate primitive is a write.
- I:HIntegrity impact, high
- The remote peer controls the decrypted payload written out-of-bounds (up to a full TLS record, roughly 16 KiB) into later iovecs while recvmsg under-reports bytes copied, giving a reliable user-space memory corruption primitive suitable for control-flow or data hijack in privileged daemons.
- A:HAvailability impact, high
- Corrupting adjacent application buffers in kTLS-enabled daemons (web proxies, storage targets, RPC endpoints) can crash workers or destabilize the service; the silent mismatch between returned length and bytes written also enables persistent denial of service on long-lived connections.