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Medium

ZEBRA: Mempool transaction admission denial via single-peer inbound queue saturation

Type: advisorySources: OSV

ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, one unauthenticated P2P peer can monopolize all 25 MAX_INBOUND_CONCURRENCY slots in Zebra's inbound mempool download and verification pipeline. In zebrad/src/components/mempool/downloads.rs, the bounded queue was shared globally without per-peer accounting, while peer identity was not carried through Gossip and FullQueue responses were mapped to Response::Nil instead of reaching overload disconnection handling. An attacker can advertise fake transaction identifiers and remain silent so each task holds a slot until TRANSACTION_DOWNLOAD_TIMEOUT, then periodically refill the queue as slots expire. While saturated, honest peer transactions and local sendrawtransaction requests are rejected with MempoolError::FullQueue, although block validation and synchronization continue. This issue is fixed in version 4.5.0.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-52732
Confirmed fixed CVEs
Not specified
Updated in this feed
7 Nov 2026, 04:14 UTC · Revision 1

Source evidence

ZEBRA: Mempool transaction admission denial via single-peer inbound queue saturation

core-osv · Original source

Published 18 Aug 2026, 19:26 UTC

ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, one unauthenticated P2P peer can monopolize all 25 MAX_INBOUND_CONCURRENCY slots in Zebra's inbound mempool download and verification pipeline. In zebrad/src/components/mempool/downloads.rs, the bounded queue was shared globally without per-peer accounting, while peer identity was not carried through Gossip and FullQueue responses were mapped to Response::Nil instead of reaching overload disconnection handling. An attacker can advertise fake transaction identifiers and remain silent so each task holds a slot until TRANSACTION_DOWNLOAD_TIMEOUT, then periodically refill the queue as slots expire. While saturated, honest peer transactions and local sendrawtransaction requests are rejected with MempoolError::FullQueue, although block validation and synchronization continue. This issue is fixed in version 4.5.0.

osv:CVE-2026-52732
Complete source record
{
  "id": "6b4c669c020a4034d815f8b4796b94ac713c88fd557403340ce6846679a15862",
  "url": "https://osv.dev/vulnerability/CVE-2026-52732",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ZEBRA: Mempool transaction admission denial via single-peer inbound queue saturation",
    "summary": "ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, one unauthenticated P2P peer can monopolize all 25 MAX_INBOUND_CONCURRENCY slots in Zebra's inbound mempool download and verification pipeline. In zebrad/src/components/mempool/downloads.rs, the bounded queue was shared globally without per-peer accounting, while peer identity was not carried through Gossip and FullQueue responses were mapped to Response::Nil instead of reaching overload disconnection handling. An attacker can advertise fake transaction identifiers and remain silent so each task holds a slot until TRANSACTION_DOWNLOAD_TIMEOUT, then periodically refill the queue as slots expire. While saturated, honest peer transactions and local sendrawtransaction requests are rejected with MempoolError::FullQueue, although block validation and synchronization continue. This issue is fixed in version 4.5.0.",
    "evidence": "osv:CVE-2026-52732",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-52732",
      "aliases": [
        "CVE-2026-52732",
        "GHSA-4fc2-h7jh-287c"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/zcashfoundation/zebra",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1440b43ca7df59aca948090d45117557b217a6cd"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "4.5.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "1440b43ca7df59aca948090d45117557b217a6cd"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "1440b43ca7df59aca948090d45117557b217a6cd"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v4.5.0"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "4.5.0"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v4.4.0",
            "v4.4.1",
            "v4.3.1",
            "4.3.1",
            "v4.3.0",
            "v4.2.0",
            "v4.1.0",
            "v4.0.0",
            "v3.1.0",
            "v3.0.0",
            "v3.0.0-rc.0",
            "v2.5.0",
            "v2.0.1",
            "v2.4.2",
            "v2.3.0",
            "v2.4.0",
            "v2.0.0",
            "v2.2.0",
            "v2.1.0",
            "v2.0.0-rc.0",
            "v1.9.0",
            "v1.8.0",
            "v1.7.0",
            "v1.6.1",
            "v1.6.0",
            "v1.5.2",
            "v1.5.1",
            "v1.5.0",
            "v1.4.0",
            "v1.3.0",
            "v1.2.0",
            "v1.1.0",
            "v1.0.1",
            "v1.0.0",
            "v1.0.0-rc.9",
            "v1.0.0-rc.8",
            "v1.0.0-rc.7",
            "v1.0.0-rc.6",
            "v1.0.0-rc.5",
            "v1.0.0-rc.0",
            "v1.0.0-rc.4",
            "v1.0.0-rc.3",
            "v1.0.0-rc.2",
            "v1.0.0-rc.1",
            "v1.0.0-beta.15",
            "v1.0.0-beta.14",
            "v1.0.0-beta.13",
            "v1.0.0-beta.12",
            "v1.0.0-beta.11",
            "v1.0.0-beta.10",
            "v1.0.0-beta.9",
            "v1.0.0-beta.8",
            "v1.0.0-beta.7",
            "v1.0.0-beta.6",
            "v1.0.0-beta.5",
            "v1.0.0-beta.4",
            "v1.0.0-beta.3",
            "v1.0.0-beta.2",
            "v1.0.0-beta.1",
            "v1.0.0-beta.0",
            "v1.0.0-alpha.19",
            "v1.0.0-alpha.18",
            "v1.0.0-alpha.17",
            "v1.0.0-alpha.16",
            "v1.0.0-alpha.15",
            "v1.0.0-alpha.14",
            "v1.0.0-alpha.13",
            "v1.0.0-alpha.12",
            "v1.0.0-alpha.11",
            "v1.0.0-alpha.10",
            "v1.0.0-alpha.9",
            "v1.0.0-alpha.8",
            "v1.0.0-alpha.7",
            "v1.0.0-alpha.6",
            "v1.0.0-alpha.5",
            "v1.0.0-alpha.4",
            "v1.0.0-alpha.3",
            "v1.0.0-alpha.2",
            "v1.0.0-alpha.1",
            "v1.0.0-alpha.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52732.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:49.448907625Z",
      "provider": "osv",
      "references": [
        "https://github.com/ZcashFoundation/zebra/releases/tag/v4.5.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52732.json",
        "https://github.com/ZcashFoundation/zebra/security/advisories/GHSA-4fc2-h7jh-287c",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-52732",
        "https://github.com/ZcashFoundation/zebra/commit/1440b43ca7df59aca948090d45117557b217a6cd"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52732.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-52732",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 518045,
  "published_at": "2026-08-18T19:26:07.345+00:00"
}