CVE-2026-68118 (GCVE-0-2026-68118)

Vulnerability from cvelistv5 – Published: 2026-08-10 11:58 – Updated: 2026-08-17 04:59
VLAI
Title
tcp: challenge ACK for non-exact RST in SYN-RECEIVED
Summary
In the Linux kernel, the following vulnerability has been resolved: tcp: challenge ACK for non-exact RST in SYN-RECEIVED The SYN-RECEIVED request-socket path in tcp_check_req() accepts an in-window RST without requiring SEG.SEQ to exactly match RCV.NXT. A non-exact RST therefore removes the request instead of eliciting a challenge ACK. RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in SYN-RECEIVED: an exact RST resets the connection, while a non-exact in-window RST must trigger a challenge ACK and be dropped. Apply that check before the ACK-field validation, following the RFC sequence-number, RST, then ACK processing order. Factor the per-netns challenge ACK quota out of tcp_send_challenge_ack() so request sockets can share it. Use the request socket's send_ack() callback and its own out-of-window ACK timestamp to send and rate-limit the response.
Severity
8.2 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 282f23c6ee343126156dd41218b22ece96d747e3 , < 234f9ffbd9b2c1b24ec67200ea3cff07401bec48 (git)
Affected: 282f23c6ee343126156dd41218b22ece96d747e3 , < 22cec809b048495310f206d9abbcdbbfbdce3ae3 (git)
Affected: 282f23c6ee343126156dd41218b22ece96d747e3 , < a28c4fcbf774e23b4779cae468e3497a5ad1f4a1 (git)
Affected: 86791bbfe5ed7b275be040cfeff049a1624af1b7 (git)
Affected: 61f69dc4e40e41b0018f00fa4aeb23d3239556fb (git)
Affected: 34fb350281ced2a72707a5c0064f69992d440edb (git)
Affected: 3.0.58 , < 3.1 (semver)
Affected: 3.2.37 , < 3.3 (semver)
Affected: 3.4.25 , < 3.5 (semver)
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Linux Linux Affected: 3.6
Unaffected: 0 , < 3.6 (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/tcp.h",
            "net/ipv4/tcp_input.c",
            "net/ipv4/tcp_minisocks.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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          "versions": [
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              "version": "61f69dc4e40e41b0018f00fa4aeb23d3239556fb",
              "versionType": "git"
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              "version": "34fb350281ced2a72707a5c0064f69992d440edb",
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              "status": "affected",
              "version": "3.2.37",
              "versionType": "semver"
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              "status": "affected",
              "version": "3.4.25",
              "versionType": "semver"
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          "product": "Linux",
          "programFiles": [
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            "net/ipv4/tcp_minisocks.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "3.6"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.42",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.42",
                  "versionStartIncluding": "3.6",
                  "vulnerable": true
                },
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: challenge ACK for non-exact RST in SYN-RECEIVED\n\nThe SYN-RECEIVED request-socket path in tcp_check_req() accepts an\nin-window RST without requiring SEG.SEQ to exactly match RCV.NXT.  A\nnon-exact RST therefore removes the request instead of eliciting a\nchallenge ACK.\n\nRFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in\nSYN-RECEIVED: an exact RST resets the connection, while a non-exact\nin-window RST must trigger a challenge ACK and be dropped.\n\nApply that check before the ACK-field validation, following the RFC\nsequence-number, RST, then ACK processing order.  Factor the per-netns\nchallenge ACK quota out of tcp_send_challenge_ack() so request sockets\ncan share it.  Use the request socket\u0027s send_ack() callback and its own\nout-of-window ACK timestamp to send and rate-limit the response."
        }
      ],
      "metrics": [
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            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H",
            "version": "3.1"
          },
          "scenarios": [
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              "lang": "en",
              "value": "AV:N - The bug is in tcp_check_req() on the core TCP receive path (ip_rcv/tcp_v4_rcv or tcp_v6_rcv \u2192 __inet_lookup_skb on TCP_NEW_SYN_RECV \u2192 tcp_check_req); any remote host that can deliver TCP segments to an internet-facing listener reaches it with no local access.\nAC:L - An attacker controls the forged RST (source/dest ports, SEQ sweep across the SYN-RECEIVED window up to tcp_synack_window/65535) and can retry on every handshake; no race, rare config, or victim-only state outside attacker influence is required beyond routine IP spoofing or on-path delivery.\nPR:N - Processing occurs on the pre-authentication TCP handshake path for embryonic request sockets; no credentials, capabilities, or local account are needed\u2014only the ability to send (or spoof) TCP packets to the target listener.\nUI:N - Handshake teardown is triggered automatically when the kernel receives the crafted RST during SYN-RECEIVED; no victim must open files, click links, or perform any other action.\nS:U - Impact is confined to incorrect TCP connection-state handling within the same host kernel; it does not cross VM, container, or IOMMU security boundaries.\nC:N - This is a protocol state-machine logic flaw with no memory corruption, out-of-bounds access, use-after-free, or information disclosure\u2014only embryonic request-socket teardown occurs.\nI:L - A non-exact in-window RST causes unauthorized modification of TCP connection state by dropping the embryonic request socket (embryonic_reset/inet_csk_reqsk_queue_drop) instead of preserving it per RFC 5961/RFC 9293.\nA:H - Repeated spoofed in-window RSTs during SYN-RECEIVED can prevent TCP handshakes from completing on arbitrary listening services (HTTPS, SSH, databases, load balancers), causing sustained denial of service without kernel crash."
            }
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      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:59:08.546Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48"
        },
        {
          "url": "https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3"
        },
        {
          "url": "https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1"
        }
      ],
      "title": "tcp: challenge ACK for non-exact RST in SYN-RECEIVED",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68118",
    "datePublished": "2026-08-10T11:58:38.000Z",
    "dateReserved": "2026-07-30T09:28:09.369Z",
    "dateUpdated": "2026-08-17T04:59:08.546Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
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      "cve": "CVE-2026-68118",
      "date": "2026-08-20",
      "epss": "0.00384",
      "percentile": "0.31749"
    },
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-13T23:14:10+00:00",
      "cve": "CVE-2026-68118",
      "id": "CVE-2026-68118",
      "initial_release_date": "2026-08-10T00:00:00+00:00",
      "product_status:known_affected": "262",
      "product_status:known_not_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: tcp: challenge ACK for non-exact RST in SYN-RECEIVED",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68118.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "low",
      "current_release_date": "2026-08-13T16:24:13Z",
      "cve": "CVE-2026-68118",
      "id": "CVE-2026-68118",
      "initial_release_date": "2026-08-13T16:24:13Z",
      "product_status:known_affected": "296",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68118",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68118.json",
      "version": "2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.