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CVE-2026-46086 (GCVE-0-2026-46086)

Vulnerability from cvelistv5 – Published: 2026-05-27 12:58 – Updated: 2026-09-08 08:49
VLAI
Title
net: bridge: use a stable FDB dst snapshot in RCU readers
Summary
In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 960b589f86c74ce582922fcb996103271081f4de , < c502fa9f094cb03d1d1685c71e2105ab359bc2b8 (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < a6ae4511c07b91f597e461406c6330f0d4ff810e (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < 1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < 0b9e4bbfb7c949151e3acd44ed4aa33614d2e110 (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < 81af4137a30c4c2dc694dea8cacb180bd66000ef (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < 5424e678f9b304e148cf5dcc047cffc7a56a3bb5 (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < 9a2d9d4e657b23dc21f24cf139e3aeff0b61341f (git)
Affected: 960b589f86c74ce582922fcb996103271081f4de , < df4601653201de21b487c3e7fffd464790cab808 (git)
guessed Create a notification for this product.
Linux Linux Affected: 3.14
Unaffected: 0 , < 3.14 (semver)
Unaffected: 5.10.259 , ≤ 5.10.* (semver)
Unaffected: 5.15.210 , ≤ 5.15.* (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.140 , ≤ 6.6.* (semver)
Unaffected: 6.12.86 , ≤ 6.12.* (semver)
Unaffected: 6.18.27 , ≤ 6.18.* (semver)
Unaffected: 7.0.4 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
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                    "matchCriteriaId": "0F91AF02-7C23-4888-A580-07C166BE8128",
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                    "vulnerable": true
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                    "vulnerable": true
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                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: use a stable FDB dst snapshot in RCU readers\n\nLocal FDB entries can be rewritten in place by `fdb_delete_local()`, which\nupdates `f-\u003edst` to another port or to `NULL` while keeping the entry\nalive. Several bridge RCU readers inspect `f-\u003edst`, including\n`br_fdb_fillbuf()` through the `brforward_read()` sysfs path.\n\nThese readers currently load `f-\u003edst` multiple times and can therefore\nobserve inconsistent values across the check and later dereference.\nIn `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change\n`f-\u003edst` after the NULL check and before the `port_no` dereference,\nleading to a NULL-ptr-deref.\n\nFix this by taking a single `READ_ONCE()` snapshot of `f-\u003edst` in each\naffected RCU reader and using that snapshot for the rest of the access\nsequence. Also publish the in-place `f-\u003edst` updates in `fdb_delete_local()`\nwith `WRITE_ONCE()` so the readers and writer use matching access patterns."
          }
        ],
        "id": "CVE-2026-46086",
        "lastModified": "2026-09-08T09:18:07.390",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 5.5,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.8,
              "impactScore": 3.6,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
          ]
        },
        "published": "2026-05-27T14:17:30.080",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/0b9e4bbfb7c949151e3acd44ed4aa33614d2e110"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a"
          },
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            "tags": [
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            ],
            "url": "https://git.kernel.org/stable/c/5424e678f9b304e148cf5dcc047cffc7a56a3bb5"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
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          },
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            "tags": [
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          },
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          },
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            "tags": [
              "Patch"
            ],
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          },
          {
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            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/df4601653201de21b487c3e7fffd464790cab808"
          },
          {
            "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
            "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Undergoing Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-476"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-28T07:42:38+00:00",
      "cve": "CVE-2026-46086",
      "id": "CVE-2026-46086",
      "initial_release_date": "2026-05-27T00:00:00+00:00",
      "product_status:fixed": "762",
      "product_status:known_affected": "64",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net: bridge: use a stable FDB dst snapshot in RCU readers",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-46086.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-16T00:12:56Z",
      "cve": "CVE-2026-46086",
      "id": "CVE-2026-46086",
      "initial_release_date": "2026-05-28T03:52:55Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "578",
      "product_status:known_not_affected": "71",
      "product_status:recommended": "380",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-46086",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-46086.json",
      "version": "18"
    }
  }
}



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Taxonomy of the tags.





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.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.