CVE-2026-43383Network attack vector

TCP authentication disclosure via variable-time MAC comparison

Published May 8, 2026 · Updated May 8, 2026

Timing side channel in Linux Kernel TCP-MD5 handling allows remote attackers to infer MAC data from affected releases via crafted packets. The TCP-MD5 receive path compares computed and received 16-byte MACs with memcmp, whose early exit exposes match-dependent timing. Reachability requires TCP-MD5 to be configured on an accessible socket; repeated timing observations can disclose authentication material and undermine packet authentication.

CVSS severity9.4
Critical
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing side channel in Linux Kernel TCP-MD5 handling allows remote attackers to infer MAC data from affected releases via crafted packets. The TCP-MD5 receive path compares computed and received 16-byte MACs with memcmp, whose early exit exposes match-dependent timing. Reachability requires TCP-MD5 to be configured on an accessible socket; repeated timing observations can disclose authentication material and undermine packet authentication.

The record

CVE
CVE-2026-43383
Published
May 8, 2026
Updated
May 8, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 8, 2026CVE publishedPublication date reported by the CVE source.
  2. May 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.6.20
  2. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <02669e2a4d207068edce7e8b5fafd85822018ce6
  3. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <345a9530756528d7ca407663d659c3c40e75c3dd
  4. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <46d0d6f50dab706637f4c18a470aac20a21900d3
  5. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <5d305a95130a8d08b9545e47f1e18d29d59866cb
  6. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <821c8751fdeecdeecabeb11704dd33439c9e4bbc
  7. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <ae3831b44f477de048287493e184fc3ff913b624
  8. Affected versionversion=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <b502e97e29d791ff7a8051f29a414535739be218

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=2.6.20; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <02669e2a4d207068edce7e8b5fafd85822018ce6; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <345a9530756528d7ca407663d659c3c40e75c3dd; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <46d0d6f50dab706637f4c18a470aac20a21900d3; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <5d305a95130a8d08b9545e47f1e18d29d59866cb; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <821c8751fdeecdeecabeb11704dd33439c9e4bbc; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <ae3831b44f477de048287493e184fc3ff913b624; version=cfb6eeb4c860592edd123fdea908d23c6ad1c7dc <b502e97e29d791ff7a8051f29a414535739be218

Published CVSS scores

9.4kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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