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CVE Record

CVE-2026-23095: gue: Fix skb memleak with inner IP protocol 0.

In the Linux kernel, the following vulnerability has been resolved: gue: Fix skb memleak with inner IP protocol 0. syzbot reported skb memleak below. [0] The repro generated a GUE packet with its inner protocol 0. gue_udp_recv() returns -guehdr->proto_ctype for "resubmit" in ip_protocol_deliver_rcu(), but this only works with non-zero protocol number. Let's drop such packets. Note that 0 is a valid number (IPv6 Hop-by-Hop Option). I think it is not practical to encap HOPOPT in GUE, so once someone starts to complain, we could pass down a resubmit flag pointer to distinguish two zeros from the upper layer: * no error * resubmit HOPOPT [0] BUG: memory leak unreferenced object 0xffff888109695a00 (size 240): comm "syz.0.17", pid 6088, jiffies 4294943096 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 40 c2 10 81 88 ff ff 00 00 00 00 00 00 00 00 .@.............. backtrace (crc a84b336f): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4958 [inline] slab_alloc_node mm/slub.c:5263 [inline] kmem_cache_alloc_noprof+0x3b4/0x590 mm/slub.c:5270 __build_skb+0x23/0x60 net/core/skbuff.c:474 build_skb+0x20/0x190 net/core/skbuff.c:490 __tun_build_skb drivers/net/tun.c:1541 [inline] tun_build_skb+0x4a1/0xa40 drivers/net/tun.c:1636 tun_get_user+0xc12/0x2030 drivers/net/tun.c:1770 tun_chr_write_iter+0x71/0x120 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x45d/0x710 fs/read_write.c:686 ksys_write+0xa7/0x170 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xa4/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-23095 is a Linux kernel memory leak in GUE packet handling. A crafted encapsulated packet with inner protocol value 0 can cause kernel socket buffer memory not to be freed. The main business risk is availability degradation or denial of service on affected Linux systems that process this traffic.

Executive priority

Prioritize routine-to-expedited patching for internet-facing, network-edge, virtualization, tunneling, or appliance systems. The issue is high severity because it can affect availability without authentication, but current sources do not show active exploitation.

Technical view

The flaw is in gue_udp_recv() handling of GUE packets with inner IP protocol 0. The resubmit return path does not work for a zero protocol number, causing an skb memory leak. The kernel fix drops such packets. CVSS is 7.5, network reachable, low complexity, no privileges, no user interaction, availability-only impact.

Likely exposure

Exposure is most likely on Linux systems running affected kernel builds with GUE processing reachable. The bundle lists Linux kernel versions and stable commits, but exact downstream distro package exposure must be confirmed through vendor advisories.

Exploitation context

The evidence cites a syzbot memory-leak report and kernel fixes. The bundle marks KEV false and provides no cited evidence of active exploitation. Treat exploitability as plausible for availability impact, but do not assume real-world exploitation from these sources alone.

Researcher notes

The root condition is inner protocol 0 in GUE. The fix behavior is to drop such packets, with source discussion noting protocol 0 is valid for IPv6 Hop-by-Hop but considered impractical for GUE encapsulation. Downstream version ranges need vendor confirmation.

Mitigation direction

  • Apply Linux kernel updates containing the referenced stable fixes.
  • Check distribution and appliance vendor advisories for packaged kernel status.
  • Review Siemens SSA-019113 if Siemens products are in scope.
  • Limit exposure of GUE-related traffic where operationally unnecessary.
  • Monitor affected systems for abnormal kernel memory growth or packet-processing instability.

Validation and detection

  • Inventory Linux kernel versions across servers, appliances, and embedded systems.
  • Map installed kernels to vendor advisories and fixed stable commits.
  • Confirm whether GUE processing or related encapsulated traffic is enabled or reachable.
  • Check vulnerability scanner findings against distro backport notes.
  • Review logs and monitoring for availability symptoms or memory pressure.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2026-23095 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-23095Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535b, 37dd0247797b168ad1cc7f5dbec825a1ee66535bunaffected
LinuxLinux3.18, 0, 5.10.249, 5.15.199, 6.1.162, 6.6.122, 6.12.68, 6.18.8, 6.19affected
Weakness

CWE details

No CWE listed

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