CVE-2020-36791 (GCVE-0-2020-36791)
Vulnerability from cvelistv5
Published
2025-05-07 13:17
Modified
2026-08-05 08:44
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net_sched: keep alloc_hash updated after hash allocation In commit 599be01ee567 ("net_sched: fix an OOB access in cls_tcindex") I moved cp->hash calculation before the first tcindex_alloc_perfect_hash(), but cp->alloc_hash is left untouched. This difference could lead to another out of bound access. cp->alloc_hash should always be the size allocated, we should update it after this tcindex_alloc_perfect_hash().
References
Impacted products
Vendor Product Version
Linux Linux Version: 73c29d2f6f8ae731b1e09051b69ed3ba2319482b
Version: b974ac51f5834a729de252fc5c1c9de9efd79b45
Version: 6cb448ee493c8a514c9afa0c346f3f5b3227de85
Version: 478c4b2ffd44e5186c7e22ae7c38a86a5b9cfde5
Version: dd8142a6fa5270783d415292ec8169f4ea2a5468
Version: 2c66ff8d08f81bcf8e8cb22e31e39c051b15336a
Version: 599be01ee567b61f4471ee8078870847d0a11e8e
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   Linux Linux Version: 4.4.214   ≤
Version: 4.9.214   ≤
Version: 4.14.171   ≤
Version: 4.19.103   ≤
Version: 5.4.19   ≤
Version: 5.5.3   ≤
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{
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          "programFiles": [
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      "cpeApplicability": [
        {
          "nodes": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: keep alloc_hash updated after hash allocation\n\nIn commit 599be01ee567 (\"net_sched: fix an OOB access in cls_tcindex\")\nI moved cp-\u003ehash calculation before the first\ntcindex_alloc_perfect_hash(), but cp-\u003ealloc_hash is left untouched.\nThis difference could lead to another out of bound access.\n\ncp-\u003ealloc_hash should always be the size allocated, we should\nupdate it after this tcindex_alloc_perfect_hash()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is triggered through the tc filter netlink configuration path (RTM_NEWTFILTER \u2192 tc_new_tfilter \u2192 tcindex_change \u2192 tcindex_set_parms), not by processing network packets. Exploitation requires local netlink/syscall access to configure cls_tcindex.\nAC:L - An attacker fully controls both the old and new hash sizes and the filter handle via netlink attributes, so shrinking a perfect hash while using a handle past the newly allocated size reliably produces the OOB access with no race or external conditions.\nPR:L - tc_new_tfilter requires CAP_NET_ADMIN checked with netlink_ns_capable against the network namespace\u0027s user_ns, which an unprivileged user can obtain via user namespaces (unshare -Urn) without real root in the init namespace.\nUI:N - The attacker creates and modifies their own tcindex filters in a network namespace they control; no victim action is required.\nS:U - Impact is confined to the host kernel privilege boundary (local memory corruption / privilege escalation) and does not cross VM, IOMMU, or other distinct security authorities.\nC:H - Stale alloc_hash allows OOB reads through tcindex_get/tcindex_lookup (perfect + handle beyond the allocated array), and the heap OOB can be leveraged for arbitrary kernel memory disclosure.\nI:H - tcindex_set_parms does r = cp-\u003eperfect + handle then writes result/exts into that slot; with handle past the newly allocated hash this is a controlled heap out-of-bounds write enabling memory corruption and control-flow hijacking.\nA:H - The out-of-bounds access was caught by syzbot as a kernel memory-safety failure and can produce oops/panic or heap corruption leading to a crash even without full exploitation."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T08:44:33.087Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/d6cdc5bb19b595486fb2e6661e5138d73a57f454"
        },
        {
          "url": "https://git.kernel.org/stable/c/c4453d2833671e3a9f6bd52f0f581056c3736386"
        },
        {
          "url": "https://git.kernel.org/stable/c/9f8b6c44be178c2498a00b270872a6e30e7c8266"
        },
        {
          "url": "https://git.kernel.org/stable/c/557d015ffb27b672e24e6ad141fd887783871dc2"
        },
        {
          "url": "https://git.kernel.org/stable/c/d23faf32e577922b6da20bf3740625c1105381bf"
        },
        {
          "url": "https://git.kernel.org/stable/c/bd3ee8fb6371b45c71c9345cc359b94da2ddefa9"
        },
        {
          "url": "https://git.kernel.org/stable/c/0d1c3530e1bd38382edef72591b78e877e0edcd3"
        },
        {
          "url": "https://syzkaller.appspot.com/bug?id=ea260693da894e7b078d18fca2c9c0a19b457534"
        },
        {
          "url": "https://blog.cdthoughts.ch/2021/03/16/syzbot-bug.html"
        }
      ],
      "title": "net_sched: keep alloc_hash updated after hash allocation",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2020-36791",
    "datePublished": "2025-05-07T13:17:33.882Z",
    "dateReserved": "2024-02-26T17:07:27.435Z",
    "dateUpdated": "2026-08-05T08:44:33.087Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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