rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion

{
  "id": "8dba37c9e8b05f9faf1a85f3a0719196c53cf386242dee165a59ce5e659845fd",
  "url": "https://osv.dev/vulnerability/CVE-2026-70455",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "rsync 3.4.2 < 3.5.0 DoS via --zt Zstandard Compression Thread Exhaustion",
    "summary": "rsync 3.4.2 before 3.5.0 contains a denial of service vulnerability that allows a remote sender to exhaust system resources by specifying the --zt short alias for --compress-threads, which bypasses the refuse options directive's string matching on long option names. Attackers can specify --zt=N with a large value to spawn an unbounded number of Zstandard worker threads on the receiver, exhausting available thread and memory resources.",
    "evidence": "osv:CVE-2026-70455",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-70455",
      "aliases": [
        "CVE-2026-70455",
        "GHSA-rjvj-qgqg-cvx9"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.samba.org/rsync.git/",
              "type": "GIT",
              "events": [
                {
                  "introduced": "de3cc03b03be153092f266aa1117b4706947ed07"
                },
                {
                  "fixed": "471e17dc0d68233db84db11be82c9f62f4661214"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:samba:rsync:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "3.4.2"
                      },
                      {
                        "fixed": "3.5.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  }
                ]
              }
            },
            {
              "repo": "https://github.com/rsyncproject/rsync",
              "type": "GIT",
              "events": [
                {
                  "introduced": "de3cc03b03be153092f266aa1117b4706947ed07"
                },
                {
                  "fixed": "471e17dc0d68233db84db11be82c9f62f4661214"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:samba:rsync:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "3.4.2"
                      },
                      {
                        "fixed": "3.5.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "471e17dc0d68233db84db11be82c9f62f4661214"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v3.5.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v3.4.3",
            "v3.4",
            "v3.4.2"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-70455.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:25.318399642Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/70xxx/CVE-2026-70455.json",
        "https://github.com/RsyncProject/rsync/releases/tag/v3.5.0",
        "https://github.com/RsyncProject/rsync/security/advisories/GHSA-rjvj-qgqg-cvx9",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-70455",
        "https://www.vulncheck.com/advisories/rsync-dos-via-zt-zstandard-compression-thread-exhaustion",
        "https://github.com/RsyncProject/rsync"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/70xxx/CVE-2026-70455.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-70455",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 492097,
  "published_at": "2026-08-13T14:45:11.164+00:00"
}