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CVE-2026-74735
l2tp: fix tunnel and session refcount leak on seq_file release
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem net/l2tp. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74735 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 | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In pppol2tp_proc_open() and l2tp_dfs_seq_open(), iteration state (pd->tunnel and pd->session) is kept in seq_file private data to allow iteration across multiple read() system calls. However, if userspace closes /proc/net/pppol2tp or /sys/kernel/debug/l2tp/tunnels before reading to end-of-file (EOF), any tunnel or session reference stored in pd->tunnel / pd->session is left un-dropped when seq_file private data is freed. Fix this by dropping any remaining pd->tunnel and pd->session references in pppol2tp_proc_release() and l2tp_dfs_seq_release() when closing the file.
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/l2tp/l2tp_debugfs.c
net/l2tp/l2tp_ppp.c
- What this is
- NETWORKING [GENERAL]MAINTAINERS section matched on net/ · netdev@vger.kernel.org · Maintained
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid, bookworm · linux-6.12?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
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
Signals
- Published
- 2026-08-26 (2 months ago)source
- CVSS
- no vector published, unrated
- Attack vector
- not published
- EPSS
- 0.18%, higher than 6.7% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/l2tp
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.17 | 6.12.111 | bdf836137819 |
| 4.17 | 6.18.53 | 8c4fde01bcf9 |
| 4.17 | 7.1.10 | ebe2774e9564 |
| 4.17 | 7.2 | 9006c116dd11 |
| 3.16.60 | 0 | 0 |
| 4.16.6 | 0 | 0 |
| 3.16.60 | 0 | 0 |
| 4.16.6 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
The kernel CNA published no CVSS vector and no reasoning for CVE-2026-74735, which is why it is shown as unrated rather than given an invented score. 6,405 of the 20,413 CVEs here carry reasoning; this is not one of them.