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CVE-2026-64009— xfrm: Check for underflow in xfrm_state_mtu

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel 2.6.22版本存在安全漏洞，该漏洞源于xfrm_state_mtu函数在下溢检查缺失，可能导致在esp组件中写入大量零字节。

CVSS 7.8 · High EPSS 0.20% · P10

Possible ATT&CK Techniques 1 AI

T1068 · Exploitation for Privilege Escalation

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux c5c2523893747f88a83376abad310c8ad13f7197< 8014f70c4e6e5ab101ae3860a614e65e988372e3 affected
c5c2523893747f88a83376abad310c8ad13f7197< 1021d2877b689a648b27815c854557a917122e93 affected
c5c2523893747f88a83376abad310c8ad13f7197< 2a41b1b31c61c52b972278ce1732a1443f5e89ed affected
c5c2523893747f88a83376abad310c8ad13f7197< fccd685b32df5aaf6bad4381eeda216468e283f0 affected
c5c2523893747f88a83376abad310c8ad13f7197< 820e501be8aee4b365d218d83227b314309c5fda affected
c5c2523893747f88a83376abad310c8ad13f7197< 82ac903e0b519849647657b8c48d21237ada06a2 affected
c5c2523893747f88a83376abad310c8ad13f7197< 3db50ceeacb52806d8fe86fb1dfe944df0b9f789 affected
c5c2523893747f88a83376abad310c8ad13f7197< 742b04d0550b0ec89dcbc99537ec88653bd1ad90 affected
… +10 more rows
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I. Basic Information for CVE-2026-64009

Vulnerability Information
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Vulnerability Title
xfrm: Check for underflow in xfrm_state_mtu
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: xfrm: Check for underflow in xfrm_state_mtu Leo Lin reported OOB write issue in esp component: xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned modulo-2^32 space using an attacker-influenced "header_len + authsize + net_adj" subtracted from a small "mtu" argument. A nobody user can install an IPv4 ESP tunnel SA with a large authentication key (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc), configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a large value. When a single UDP datagram is then sent through the tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and esp_output() consumes it as a signed int via: padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached)) esp.tfclen = padto - skb->len (assigned to int) esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t when passed to memset() inside esp_output_fill_trailer(), producing a ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as "Write of size 18446744073709551537 at addr ffff888...". Check for underflow and return 1. This causes the sendmsg attempt to fail with ENETUNREACH.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel 2.6.22版本存在安全漏洞，该漏洞源于xfrm_state_mtu函数在下溢检查缺失，可能导致在esp组件中写入大量零字节。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux c5c2523893747f88a83376abad310c8ad13f7197 ~ 8014f70c4e6e5ab101ae3860a614e65e988372e3 -
Linux Linux 2.6.22 -

II. Public POCs for CVE-2026-64009

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III. Intelligence Information for CVE-2026-64009

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Patches & Fixes for CVE-2026-64009 (7)

Same Patch Batch · Linux · 2026-07-19 · 429 CVEs total

CVE-2026-63795 10.0 CRITICAL 9p: avoid putting oldfid in p9_client_walk() error path
CVE-2026-64068 9.8 CRITICAL netfs: Fix missing locking around retry adding new subreqs
CVE-2026-63993 9.8 CRITICAL vxlan: do not reuse cached ip_hdr() value after skb_tunnel_check_pmtu()
CVE-2026-64142 9.8 CRITICAL ksmbd: close durable scavenger races against m_fp_list lookups
CVE-2026-64033 9.8 CRITICAL RDMA/rtrs: Fix use-after-free in path file creation cleanup
CVE-2026-53399 9.8 CRITICAL nfsd: release layout stid on setlease failure
CVE-2026-53398 9.8 CRITICAL NFSD: Fix SECINFO_NO_NAME decode error cleanup
CVE-2026-64061 9.8 CRITICAL netfs: Fix early put of sink folio in netfs_read_gaps()
CVE-2026-64025 9.8 CRITICAL bpf, skmsg: fix verdict sk_data_ready racing with ktls rx
CVE-2026-64089 9.8 CRITICAL batman-adv: tt: fix negative last_changeset_len
CVE-2026-64125 9.8 CRITICAL net: bcmgenet: keep RBUF EEE/PM disabled
CVE-2026-64091 9.8 CRITICAL batman-adv: tt: fix TOCTOU race for reported vlans
CVE-2026-64066 9.8 CRITICAL netfs: Fix netfs_read_to_pagecache() to pause on subreq failure
CVE-2026-63887 9.8 CRITICAL scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf
CVE-2026-63808 9.8 CRITICAL exfat: fix potential use-after-free in exfat_find_dir_entry()
CVE-2026-63978 9.8 CRITICAL net/handshake: Drain pending requests at net namespace exit
CVE-2026-64132 9.8 CRITICAL ipv6: ioam: refresh hdr pointer before ioam6_event()
CVE-2026-63979 9.8 CRITICAL net/handshake: hand off the pinned file reference to accept_doit
CVE-2026-64136 9.8 CRITICAL smb: client: protect tc_count increment in smb2_find_smb_sess_tcon_unlocked()
CVE-2026-63800 9.8 CRITICAL pNFS: Fix use-after-free in pnfs_update_layout()

Showing top 20 of 429 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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