CyberSecBulletin
CVE-2026-46099NVD status: Modified

Linux: Use After Free

Published Updated By the CyberSecBulletin desk

CVE-2026-46099 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 51fef5a7c4d160839199e941929456ba21ddf73c, b258b849a580285a1692e782ebc902b44c884a71, 6bd17925bd6866027a6555db17905b9fc073d38d as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.22% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to 51fef5a7c4d160839199e941929456ba21ddf73c or b258b849a580285a1692e782ebc902b44c884a71 or 6bd17925bd6866027a6555db17905b9fc073d38d or 52f9db67f8f35f436366cf4980b4f0a2583d0ef0, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.15.209 or 6.1.175 or 6.6.140 or 6.12.86, whichever matches your release line, or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxaf4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, 51fef5a7c4d160839199e941929456ba21ddf73c; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, b258b849a580285a1692e782ebc902b44c884a71; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, 6bd17925bd6866027a6555db17905b9fc073d38d; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, 52f9db67f8f35f436366cf4980b4f0a2583d0ef0; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, b778b6d095421619c331fd2d7751143cd5387103; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, 9dd5481f960e337b81d7dfe429529495c1c481c0; af4a2209b1344939eaac11f269c261d347cbc3ee up to, but not including, f9c52a6ba9780bd27e0bf4c044fd91c13c778b6e; 4.1251fef5a7c4d160839199e941929456ba21ddf73c, b258b849a580285a1692e782ebc902b44c884a71, 6bd17925bd6866027a6555db17905b9fc073d38d, 52f9db67f8f35f436366cf4980b4f0a2583d0ef0, b778b6d095421619c331fd2d7751143cd5387103, 9dd5481f960e337b81d7dfe429529495c1c481c0
Red HatRed Hat Enterprise Linux 10Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 10.0 Extended Update SupportNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP SolutionsNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9.6 Extended Update SupportNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 6Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 7Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 8Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9Not specified in the recordNot stated
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel4.12 up to, but not including, 5.15.209; 5.16 up to, but not including, 6.1.175; 6.2 up to, but not including, 6.6.140; 6.7 up to, but not including, 6.12.86; 6.13 up to, but not including, 6.18.27; 6.19 up to, but not including, 7.0.4; 7.15.15.209, 6.1.175, 6.6.140, 6.12.86, 6.18.27, 7.0.4

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
HighSuccess depends on conditions outside the attacker's control.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Scoring systemScoreSeverityScored by
CVSS 3.18.1HighCNA
CVSS 3.17.3HighCNA

Official description

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix NOREF dst use in seg6 and rpl lwtunnels seg6_input_core() and rpl_input() call ip6_route_input() which sets a NOREF dst on the skb, then pass it to dst_cache_set_ip6() invoking dst_hold() unconditionally. On PREEMPT_RT, ksoftirqd is preemptible and a higher-priority task can release the underlying pcpu_rt between the lookup and the caching through a concurrent FIB lookup on a shared nexthop. Simplified race sequence: ksoftirqd/X higher-prio task (same CPU X) ----------- -------------------------------- seg6_input_core(,skb)/rpl_input(skb) dst_cache_get() -> miss ip6_route_input(skb) -> ip6_pol_route(,skb,flags) [RT6_LOOKUP_F_DST_NOREF in flags] -> FIB lookup resolves fib6_nh [nhid=N route] -> rt6_make_pcpu_route() [creates pcpu_rt, refcount=1] pcpu_rt->sernum = fib6_sernum [fib6_sernum=W] -> cmpxchg(fib6_nh.rt6i_pcpu, NULL, pcpu_rt) [slot was empty, store succeeds] -> skb_dst_set_noref(skb, dst) [dst is pcpu_rt, refcount still 1] rt_genid_bump_ipv6() -> bumps fib6_sernum [fib6_sernum from W to Z] ip6_route_output() -> ip6_pol_route() -> FIB lookup resolves fib6_nh [nhid=N] -> rt6_get_pcpu_route() pcpu_rt->sernum != fib6_sernum [W <> Z, stale] -> prev = xchg(rt6i_pcpu, NULL) -> dst_release(prev) [prev is pcpu_rt, refcount 1->0, dead] dst = skb_dst(skb) [dst is the dead pcpu_rt] dst_cache_set_ip6(dst) -> dst_hold() on dead dst -> WARN / use-after-free For the race to occur, ksoftirqd must be preemptible (PREEMPT_RT without PREEMPT_RT_NEEDS_BH_LOCK) and a concurrent task must be able to release the pcpu_rt. Shared nexthop objects provide such a path, as two routes pointing to the same nhid share the same fib6_nh and its rt6i_pcpu entry. Fix seg6_input_core() and rpl_input() by calling skb_dst_force() after ip6_route_input() to force the NOREF dst into a refcounted one before caching. The output path is not affected as ip6_route_output() already returns a refcounted dst.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

How developers prevent this class of flaw

  • Choose a language that provides automatic memory management.
  • When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.

More Use After Free vulnerabilities (CWE-416)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Use After Free vulnerabilities

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