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Medium

AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion

Type: advisorySources: OSV

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Version 2.23.0 contains an incomplete fix for CVE-2026-45309 in SSHServerConfig._set_tokens that blocks /, , and .. before %u substitution in AuthorizedKeysFile but does not block a leading ~ or ${ENV}, allowing later expansion in _expand_val and Path(filename).expanduser() to escape the intended authorized-keys directory. This issue is fixed in version 2.23.1.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-54590
Confirmed fixed CVEs
Not specified
Updated in this feed
3 Nov 2026, 13:31 UTC · Revision 1

Source evidence

AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion

core-osv · Original source

Published 8 Jul 2026, 20:36 UTC

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Version 2.23.0 contains an incomplete fix for CVE-2026-45309 in SSHServerConfig._set_tokens that blocks /, , and .. before %u substitution in AuthorizedKeysFile but does not block a leading ~ or ${ENV}, allowing later expansion in _expand_val and Path(filename).expanduser() to escape the intended authorized-keys directory. This issue is fixed in version 2.23.1.

osv:CVE-2026-54590
Complete source record
{
  "id": "8f5efa1fc3507b0811245bca56a42d7c4f8f82278c08d8e9ce93d961895f0154",
  "url": "https://osv.dev/vulnerability/CVE-2026-54590",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "AsyncSSH AuthorizedKeysFile username substitution bypass through ~ and environment expansion",
    "summary": "AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Version 2.23.0 contains an incomplete fix for CVE-2026-45309 in SSHServerConfig._set_tokens that blocks /, , and .. before %u substitution in AuthorizedKeysFile but does not block a leading ~ or ${ENV}, allowing later expansion in _expand_val and Path(filename).expanduser() to escape the intended authorized-keys directory. This issue is fixed in version 2.23.1.",
    "evidence": "osv:CVE-2026-54590",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-54590",
      "aliases": [
        "CVE-2026-54590",
        "GHSA-qr67-gv47-xwwh",
        "PYSEC-2026-3809"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/ronf/asyncssh",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "1b5839f3827f7bf546fc311cc8da77788a9d22f7"
                },
                {
                  "fixed": "3d515ba9ba0cd9990d248bdf62bcf05d51261a88"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.23.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "3d515ba9ba0cd9990d248bdf62bcf05d51261a88"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "1b5839f3827f7bf546fc311cc8da77788a9d22f7"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "v2.23.1"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.23.0",
            "v2.22.0",
            "v2.21.1",
            "v2.21.0",
            "v2.20.0",
            "v2.19.0",
            "v2.18.0",
            "v2.17.0",
            "v2.16.0",
            "v2.15.0",
            "v2.14.2",
            "v2.14.1",
            "v2.14.0",
            "v2.13.2",
            "v2.13.1",
            "v2.13.0",
            "v2.12.0",
            "v2.11.0",
            "v2.10.1",
            "v2.10.0",
            "v2.9.0",
            "v2.8.1",
            "v2.8.0",
            "v2.7.2",
            "v2.7.1",
            "v2.7.0",
            "v2.6.0",
            "v2.5.0",
            "v2.4.2",
            "v2.4.1",
            "v2.4.0",
            "v2.3.0",
            "v2.2.1",
            "v2.2.0",
            "v2.1.0",
            "v2.0.1",
            "v2.0.0",
            "v1.18.0",
            "v1.17.1",
            "v1.17.0",
            "v1.16.1",
            "v1.16.0",
            "v1.15.1",
            "v1.15.0",
            "v1.14.0",
            "v1.13.3",
            "v1.13.2",
            "v1.13.1",
            "v1.13.0",
            "v1.12.2",
            "v1.12.1",
            "v1.12.0",
            "v1.11.1",
            "v1.11.0",
            "v1.10.1",
            "v1.10.0",
            "v1.9.0",
            "v1.8.1",
            "v1.8.0",
            "v1.7.3",
            "v1.7.2",
            "v1.7.1",
            "v1.6.2",
            "v1.6.1",
            "v1.6.0",
            "v1.5.6",
            "v1.5.5",
            "v1.5.4",
            "v1.5.3",
            "v1.5.2",
            "v1.5.1",
            "v1.5.0",
            "v1.4.1",
            "v1.4.0",
            "v1.3.2",
            "v1.3.1",
            "v1.3.0",
            "v1.2.1",
            "v1.2.0",
            "v1.1.1",
            "v1.1.0",
            "v1.0.1",
            "v1.0.0",
            "v0.9.2",
            "v0.9.1",
            "v0.9.0",
            "v0.8.4",
            "v0.8.3",
            "v0.8.2",
            "v0.8.1",
            "v0.8.0",
            "v0.7.0",
            "v0.6.0",
            "v0.5.0",
            "v0.4.0",
            "v0.3.0",
            "v0.2.0",
            "v0.1.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54590.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.984422352Z",
      "provider": "osv",
      "references": [
        "https://github.com/ronf/asyncssh/releases/tag/v2.23.1",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54590.json",
        "https://github.com/ronf/asyncssh/security/advisories/GHSA-qr67-gv47-xwwh",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-54590",
        "https://github.com/ronf/asyncssh/commit/3d515ba9ba0cd9990d248bdf62bcf05d51261a88"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-22",
          "CWE-639"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54590.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-54590",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 495892,
  "published_at": "2026-07-08T20:36:45.258+00:00"
}