xfrm: Check for underflow in xfrm_state_mtu

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Summary

CVECVE-2026-64009
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 16:17:40 UTC
Updated2026-07-20 15:17:02 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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

EPSS: 0.002120000 probability, percentile 0.115450000 (date 2026-07-20)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 8014f70c4e6e5ab101ae3860a614e65e988372e3 git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 1021d2877b689a648b27815c854557a917122e93 git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 2a41b1b31c61c52b972278ce1732a1443f5e89ed git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 fccd685b32df5aaf6bad4381eeda216468e283f0 git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 820e501be8aee4b365d218d83227b314309c5fda git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 82ac903e0b519849647657b8c48d21237ada06a2 git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 3db50ceeacb52806d8fe86fb1dfe944df0b9f789 git Not specified
CNA Linux Linux affected c5c2523893747f88a83376abad310c8ad13f7197 742b04d0550b0ec89dcbc99537ec88653bd1ad90 git Not specified
CNA Linux Linux affected 2.6.22 Not specified
CNA Linux Linux unaffected 2.6.22 semver Not specified
CNA Linux Linux unaffected 5.10.259 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.210 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.176 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.143 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.93 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.35 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.12 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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