CVE-2026-99076

ipv6: udp: Create exceptions before socket matching

Products / packages Linux

Published 23/10/2026, 12:23:19 UTC

Severity and exploitation

Not in CISA KEVNo CVSS score

KEV coverage does not rule out exploitation.

KEV checked 14/11/2026, 21:25:33 UTC

Severity

unknown

CVSS measures technical severity, not the likelihood of an attack.

Known exploitation

Not listed in the checked CISA KEV catalog

Absence from CISA KEV does not rule out attacks.

Public exploit

Not established by this record

Missing evidence does not mean no public exploit exists.

Remediation

Fix status not established

No structured fix or guidance is available here. Check the latest publisher advisory.

What this means

In the Linux kernel, the following vulnerability has been resolved:

Source excerpt · Linux

Attack conditions

No attack-condition excerpt has been identified here. Review the full source description and references for authentication, network access, and configuration requirements.

Review supporting sources →

Affected versions

Check the exact model, release, and any platform requirements against your installation.

Linux · Linux

Linux

4 ranges

Linux version evidence

Check a product version

Compare with this publisher’s ranges. This does not inspect your installation.

affected

2b760fcf5cfb34e8610df56d83745b2b74ae1379 → before 9b88f0fcbd4b746de0478b4fd99fa495eb26b857

git versions

2b760fcf5cfb34e8610df56d83745b2b74ae1379 → before fc1fc874ceed4db566a5efbff39313d3d91d424a

git versions

2b760fcf5cfb34e8610df56d83745b2b74ae1379 → before 8c9b310c958be33ba8fb9d0e6b77811d013e10c0

git versions

2b760fcf5cfb34e8610df56d83745b2b74ae1379 → before ac76cab50e899a7346408b8d3c3a4192c2eefb9f

git versions

Other versions: unaffected

Linux · Linux

Linux

6 ranges

Linux version evidence

Check a product version

Compare with this publisher’s ranges. This does not inspect your installation.

affected

4.15

unaffected

0 → before 4.15

semver versions

6.12.117 → through 6.12.*

semver versions

6.18.61 → through 6.18.*

semver versions

7.2.11 → through 7.2.*

semver versions

7.3 → through *

original_commit_for_fix versions

Other versions: affected

Automatic dependency matching is unavailable for this record. Use the product evidence and publisher’s instructions to check your installation.

What to do

Compare your installed product and version with the affected versions above. A matching product name alone does not confirm exposure.

No structured fix or remediation guidance is available here. Check the full source description and vendor’s latest advisory for a patch or workaround; do not assume another version is safe.

cve.new guidance unless attributed to a publisher. This page does not inspect your installation.

Public exploit evidence

No public exploit reference is identified in the imported evidence. This is not a claim that no exploit exists.

Original source description

Read the full publisher description

In the Linux kernel, the following vulnerability has been resolved:

ipv6: udp: Create exceptions before socket matching

Currently, when ICMPv6 Packet Too Big and Redirect Message packets are locally delivered and quote a UDP packet, an exception is only created in the IPv6 exception cache if the kernel can match the UDP packet to an existing socket.

This behavior allows off-path attackers to conduct a side-channel attack on the exception cache in order to discover the ephemeral port used by a connected UDP socket.

Commit 4785305c05b2 ("ipv6: use siphash in rt6_exception_hash()") and commit a00df2caffed ("ipv6: make exception cache less predictible") tried to mitigate such attacks by making it harder for attackers to discover hash collisions in the exception cache and by randomizing the number of exceptions a hash bucket can hold, respectively. Unfortunately, both of the mitigations can be bypassed.

Instead, mitigate such attacks by always creating an exception, even before trying to find a matching socket. Do that by calling ip6_update_pmtu() and ip6_redirect(), the helpers used when the quoted packet did not originate from a socket.

This means that guesses (right or wrong) from an off-path attacker will always result in an exception being created or updated in the cache that the attacker can observe.

Pass the ifindex of the ingress device and the default uid, in a similar fashion to icmpv6_err(). Unlike IPv4, an oif of 0 would not match any nexthop in ip6_redirect_nh_match() and no exception would be created in response to a Redirect Message.

Note that this does not allow attackers to create exceptions that they could not create before, as both helpers can already be reached with little to no validation. For example, by sending an ICMPv6 error that quotes an ICMPv6 Echo Reply or one that quotes a UDP source port that matches a wildcard socket.

Also note that in the good case (matched socket) the above scheme comes at the cost of an extra route lookup, as the no socket helpers perform their own lookup before the one performed by ip6_sk_update_pmtu() / ip6_sk_redirect(). When the two resolve to different nexthops, it also results in two exceptions being created for the same destination IP. One in the exception cache of the nexthop resolved by the no socket helpers and another in the exception cache of the nexthop used by the socket.

References

4 sources

git.kernel.org/stable/c/9b88f0fcbd4b746de0478b4fd99fa495eb26b857

Source referenceLinux

git.kernel.org/stable/c/fc1fc874ceed4db566a5efbff39313d3d91d424a

Source referenceLinux

git.kernel.org/stable/c/8c9b310c958be33ba8fb9d0e6b77811d013e10c0

Source referenceLinux

git.kernel.org/stable/c/ac76cab50e899a7346408b8d3c3a4192c2eefb9f

Source referenceLinux

Inside the record

Evidence available

Package identity · not supplied

Version evidence

Remediation guidance · not supplied

Weakness classification · not supplied

Additional publishers · not supplied

Describes the evidence in this view, not whether the product is safe.

Original records

CVE-2026-99076

View the latest unmodified CVE JSON from the official source. It may be newer than this imported page.

cve.new JSON →

Environment requirements

These conditions apply together as specified by the publisher. A matching product name alone does not establish exposure.

Linux · platform conditions

Any condition may hold

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 4.15

After:

Through (inclusive):

Before: 6.12.117

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 4.15

After:

Through (inclusive):

Before: 6.18.61

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 4.15

After:

Through (inclusive):

Before: 7.2.11

Vulnerable product

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

From (inclusive): 4.15

After:

Through (inclusive):

Before: 7.3

Applicability preview

[
  {
    "nodes": [
      {
        "operator": "OR",
        "negate": false,
        "cpeMatch": [
          {
            "vulnerable": true,
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionStartIncluding": "4.15",
            "versionEndExcluding": "6.12.117"
          },
          {
            "vulnerable": true,
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionStartIncluding": "4.15",
            "versionEndExcluding": "6.18.61"
          },
          {
            "vulnerable": true,
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionStartIncluding": "4.15",
            "versionEndExcluding": "7.2.11"
          },
          {
            "vulnerable": true,
            "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
            "versionStartIncluding": "4.15",
            "versionEndExcluding": "7.3"
          }
        ]
      }
    ]
  }
]

Contributing organizations · 1

Linux

Assigning organization

2026-11-10

Timeline

All times UTC

23 Oct 2026, 12:23
Advisory published
Publication date supplied by the source.
10 Nov 2026, 18:15
Source updated
Latest modification date supplied by the source.
10 Nov 2026, 18:25
Last imported by cve.new
Latest catalog import, not the date we first saw this advisory.

What changed

Follow changes

CVE · CVE-2026-990762026-11-10

Observed 2026-11-10T18:25:35.575Z · upstream updated 2026-11-10T18:15:23.412Z

Product or version evidence changed

before

[
  {
    "vendor": "Linux",
    "name": "Linux",
    "platforms": [],
    "versions": [
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "fc1fc874ceed4db566a5efbff39313d3d91d424a",
        "versionType": "git"
      },
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "8c9b310c958be33ba8fb9d0e6b77811d013e10c0",
        "versionType": "git"
      },
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "ac76cab50e899a7346408b8d3c3a4192c2eefb9f",
        "versionType": "git"
      }
    ],
    "defaultStatus": "unaffected",
    "cpes": [],
    "source": "Linux",
    "url": "https://www.cve.org/CVERecord?id=CVE-2026-99076"
  },
  {
    "vendor": "Linux",
    "name": "Linux",
    "platforms": [],
    "versions": [
      {
        "version": "4.15",
        "status": "affected"
      },
      {
        "version": "0",
        "status": "unaffected",
        "lessThan": "4.15",
        "versionType": "semver"
      },
      {
        "version": "6.18.61",
        "status": "unaffected",
        "lessThanOrEqual": "6.18.*",
        "versionType": "semver"
      },
      {
        "version": "7.2.11",
        "status": "unaffected",
        "lessThanOrEqual": "7.2.*",
        "versionType": "semver"
      },
      {
        "version": "7.3",
        "status": "unaffected",
        "lessThanOrEqual": "*",
        "versionType": "original_commit_for_fix"
      }
    ],
    "defaultStatus": "affected",
    "cpes": [],
    "source": "Linux",
    "url": "https://www.cve.org/CVERecord?id=CVE-2026-99076"
  }
]

after

[
  {
    "vendor": "Linux",
    "name": "Linux",
    "platforms": [],
    "versions": [
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "9b88f0fcbd4b746de0478b4fd99fa495eb26b857",
        "versionType": "git"
      },
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "fc1fc874ceed4db566a5efbff39313d3d91d424a",
        "versionType": "git"
      },
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "8c9b310c958be33ba8fb9d0e6b77811d013e10c0",
        "versionType": "git"
      },
      {
        "version": "2b760fcf5cfb34e8610df56d83745b2b74ae1379",
        "status": "affected",
        "lessThan": "ac76cab50e899a7346408b8d3c3a4192c2eefb9f",
        "versionType": "git"
      }
    ],
    "defaultStatus": "unaffected",
    "cpes": [],
    "source": "Linux",
    "url": "https://www.cve.org/CVERecord?id=CVE-2026-99076"
  },
  {
    "vendor": "Linux",
    "name": "Linux",
    "platforms": [],
    "versions": [
      {
        "version": "4.15",
        "status": "affected"
      },
      {
        "version": "0",
        "status": "unaffected",
        "lessThan": "4.15",
        "versionType": "semver"
      },
      {
        "version": "6.12.117",
        "status": "unaffected",
        "lessThanOrEqual": "6.12.*",
        "versionType": "semver"
      },
      {
        "version": "6.18.61",
        "status": "unaffected",
        "lessThanOrEqual": "6.18.*",
        "versionType": "semver"
      },
      {
        "version": "7.2.11",
        "status": "unaffected",
        "lessThanOrEqual": "7.2.*",
        "versionType": "semver"
      },
      {
        "version": "7.3",
        "status": "unaffected",
        "lessThanOrEqual": "*",
        "versionType": "original_commit_for_fix"
      }
    ],
    "defaultStatus": "affected",
    "cpes": [],
    "source": "Linux",
    "url": "https://www.cve.org/CVERecord?id=CVE-2026-99076"
  }
]

References changed

before

[
  "https://git.kernel.org/stable/c/fc1fc874ceed4db566a5efbff39313d3d91d424a",
  "https://git.kernel.org/stable/c/8c9b310c958be33ba8fb9d0e6b77811d013e10c0",
  "https://git.kernel.org/stable/c/ac76cab50e899a7346408b8d3c3a4192c2eefb9f"
]

after

[
  "https://git.kernel.org/stable/c/9b88f0fcbd4b746de0478b4fd99fa495eb26b857",
  "https://git.kernel.org/stable/c/fc1fc874ceed4db566a5efbff39313d3d91d424a",
  "https://git.kernel.org/stable/c/8c9b310c958be33ba8fb9d0e6b77811d013e10c0",
  "https://git.kernel.org/stable/c/ac76cab50e899a7346408b8d3c3a4192c2eefb9f"
]

Environment requirements changed

before

[
  {
    "source": "Linux",
    "statements": [
      {
        "nodes": [
          {
            "operator": "OR",
            "negate": false,
            "cpeMatch": [
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "6.18.61"
              },
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "7.2.11"
              },
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "7.3"
              }
            ]
          }
        ]
      }
    ]
  }
]

after

[
  {
    "source": "Linux",
    "statements": [
      {
        "nodes": [
          {
            "operator": "OR",
            "negate": false,
            "cpeMatch": [
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "6.12.117"
              },
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "6.18.61"
              },
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "7.2.11"
              },
              {
                "vulnerable": true,
                "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                "versionStartIncluding": "4.15",
                "versionEndExcluding": "7.3"
              }
            ]
          }
        ]
      }
    ]
  }
]

Large field values are marked as truncated previews. Original source snapshots remain retained.

Showing up to 50 most recent observed changes.

Reading the signals

Severity · CVSS: Technical impact and attack conditions. No numeric assessment supplied.
Observed exploitation · KEV: An absent or unavailable KEV listing does not establish that exploitation has not occurred.
Predicted exploitation · EPSS: 0.15% estimated probability in the next 30 days. 2026-11-06 · FIRST EPSS.

Record identifiers

Aliases: None recorded

Source evidence

Request a correction or dispute

Start with the assigning organization for this record. Include the CVE ID, the disputed information, and supporting evidence. A dispute does not itself reject a record.

Find the responsible CNA →Official dispute and escalation process ↗

CVE CVE-2026-99076