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

Vulnerability from cvelistv5 – Published: 2026-04-25 08:46 – Updated: 2026-11-10 12:45
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
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-16 15:12 UTC
CWE
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6641 records in the last 180 days details
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 (6ES7518-4AX00-1AB0) Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) Affected: V3.1.7 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) Affected: V3.1.7 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) Affected: V3.1.7 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) Affected: V3.1.6 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) Affected: V3.1.5 , < * (custom)
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Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) Affected: V3.1.7 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) Affected: V3.1.6 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) Affected: V3.1.5 , < * (custom)
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Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) Affected: V3.1.7 , < * (custom)
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        "descriptions": [
          {
            "lang": "en",
            "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."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnet: ipv6: flowlabel: aplazar la liberaci\u00f3n de la opci\u00f3n exclusiva hasta el desmontaje de RCU\n\n\u2019ip6fl_seq_show()\u2019 recorre el hash global de flowlabel bajo el bloqueo de lectura de RCU del archivo seq e imprime \u2019fl  -\u003e  opt  -\u003e  opt_nflen\u2019 cuando un bloque de opci\u00f3n est\u00e1 presente.\n\nLos flowlabels exclusivos actualmente liberan \u2019fl  -\u003e  opt\u2019 tan pronto como \u2019fl  -\u003e  users\u2019 cae a cero en \u2019fl_release()\u2019. Sin embargo, la \u2019struct ip6_flowlabel\u2019 circundante permanece visible en la tabla hash global hasta que una recolecci\u00f3n de basura posterior la elimine y \u2019fl_free_rcu()\u2019 finalmente la desmonte.\n\nUn lector concurrente de \u2019/proc/ net/ip6_flowlabel\u2019 puede, por lo tanto, competir con esa \u2019kfree()\u2019 temprana y desreferenciar el estado de opci\u00f3n liberado, lo que provoca un fallo en \u2019ip6fl_seq_show()\u2019.\n\nSoluciona esto manteniendo \u2019fl  -\u003e  opt\u2019 vivo hasta \u2019fl_free_rcu()\u2019. Eso coincide con la vida \u00fatil ya requerida para el flowlabel que lo contiene mientras los lectores a\u00fan pueden acceder a \u00e9l bajo RCU."
          }
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        "id": "CVE-2026-31680",
        "lastModified": "2026-11-11T23:10:00.263",
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                "baseScore": 7.8,
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                "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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                "role": "CISA Coordinator",
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Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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