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CVE-2026-31680 (GCVE-0-2026-31680)

Vulnerability from cvelistv5 – Published: 2026-04-25 08:46 – Updated: 2026-09-08 08:48
VLAI
Title
net: ipv6: flowlabel: defer exclusive option free until RCU teardown
Summary
In the Linux kernel, the following vulnerability has been resolved: net: ipv6: flowlabel: defer exclusive option free until RCU teardown `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file RCU read-side lock and prints `fl->opt->opt_nflen` when an option block is present. Exclusive flowlabels currently free `fl->opt` as soon as `fl->users` drops to zero in `fl_release()`. However, the surrounding `struct ip6_flowlabel` remains visible in the global hash table until later garbage collection removes it and `fl_free_rcu()` finally tears it down. A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that early `kfree()` and dereference freed option state, triggering a crash in `ip6fl_seq_show()`. Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches the lifetime already required for the enclosing flowlabel while readers can still reach it under RCU.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 4b6798024f7b2d535f3db1002c760143cdbd1bd3 (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827 (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 5a6b15f861b7c1304949e3350d23490a5fe429fd (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8 (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 8027964931785cb73d520ac70a342a3dc16c249b (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 414726b69921fe6355ae453f5b35e68dd078342a (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 572ce62778519a7d4d1c15f55dd2e45a474133c4 (git)
Affected: d3aedd5ebd4b0b925b0bcda548066803e1318499 , < 9ca562bb8e66978b53028fa32b1a190708e6a091 (git)
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Linux Linux Affected: 3.9
Unaffected: 0 , < 3.9 (semver)
Unaffected: 5.10.253 , ≤ 5.10.* (semver)
Unaffected: 5.15.203 , ≤ 5.15.* (semver)
Unaffected: 6.1.168 , ≤ 6.1.* (semver)
Unaffected: 6.6.134 , ≤ 6.6.* (semver)
Unaffected: 6.12.81 , ≤ 6.12.* (semver)
Unaffected: 6.18.22 , ≤ 6.18.* (semver)
Unaffected: 6.19.12 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
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            "source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: flowlabel: defer exclusive option free until RCU teardown\n\n`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file\nRCU read-side lock and prints `fl-\u003eopt-\u003eopt_nflen` when an option block\nis present.\n\nExclusive flowlabels currently free `fl-\u003eopt` as soon as `fl-\u003eusers`\ndrops to zero in `fl_release()`. However, the surrounding\n`struct ip6_flowlabel` remains visible in the global hash table until\nlater garbage collection removes it and `fl_free_rcu()` finally tears it\ndown.\n\nA concurrent `/proc/net/ip6_flowlabel` reader can therefore race that\nearly `kfree()` and dereference freed option state, triggering a crash\nin `ip6fl_seq_show()`.\n\nFix this by keeping `fl-\u003eopt` alive until `fl_free_rcu()`. That matches\nthe lifetime already required for the enclosing flowlabel while readers\ncan still reach it under RCU."
          }
        ],
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        "metrics": {
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                "attackVector": "LOCAL",
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                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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          {
            "description": [
              {
                "lang": "en",
                "value": "NVD-CWE-noinfo"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
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    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-07-02T17:15:15+00:00",
      "cve": "CVE-2026-31680",
      "id": "CVE-2026-31680",
      "initial_release_date": "2026-04-25T00:00:00+00:00",
      "product_status:known_affected": "260",
      "product_status:known_not_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net: ipv6: flowlabel: defer exclusive option free until RCU teardown",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31680.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-11T01:29:24Z",
      "cve": "CVE-2026-31680",
      "id": "CVE-2026-31680",
      "initial_release_date": "2026-04-26T01:52:39Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "661",
      "product_status:known_not_affected": "4",
      "product_status:recommended": "316",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-31680",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-31680.json",
      "version": "20"
    }
  }
}



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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.