PT-2026-121946
CVE-2026-98969
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Published
2026-10-23
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Updated
2026-10-23
Description by
Score
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In the Linux kernel, the following vulnerability has been resolved:
net/sched: em text: reject unterminated algo before autoload
This is a follow-up to commit 9c572a83037a ("net/sched: fix potential
stack infoleak in em text dump()"), which zero-initialised the dump-side
struct. Sashiko pointed at a pre-existing bug that exposed the change-side
input-validation gap open.
em text change() casts the raw netlink attribute payload to struct
tcf em text and passes conf->algo, a 16-byte array with no enforced NUL
terminator, to textsearch prepare(). On the TS AUTOLOAD retry
textsearch prepare() calls request module("ts %s", algo); vsnprintf()
walks %s until it finds a NUL, so an algo[] with no NUL reads past the
array into the adjacent struct fields and payload and feeds those bytes
to the usermode helper command line. This is an out-of-bounds read and
a kernel memory disclosure.
Reject the attribute when no NUL exists within TC EM TEXT ALGOSIZ bytes,
matching the check xt string has had since 3ab720881b6e.
Conditions to recreate the bug:
- CAP NET ADMIN on the target netns (namespace-local via unshare -Urn is enough)
- install clsact on an interface, then add a basic filter with one text ematch whose algo[] is 16 bytes with no NUL (e.g. "A"*16) and pattern len at least 1
- the add fails with -ENOENT and the kernel invokes modprobe with a module name made of "ts " plus the 16 bytes and the adjacent payload
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