BREW-CORE-LIGHTNING-CVE-… (GHSA-V92G-XGXW-VVMM)

Vulnerability from osv_homebrew – Published: 2026-08-13 16:41 – Updated: 2026-09-12 08:48 – Source website
VLAI
Summary
Mako: Path traversal via double-slash URI prefix in TemplateLookup
Details

Summary

TemplateLookup.get_template() is vulnerable to path traversal when a URI starts with // (e.g., //../../../secret.txt). The root cause is an inconsistency between two slash-stripping implementations:

  • Template.__init__ strips one leading / using if/slice
  • TemplateLookup.get_template() strips all leading / using re.sub(r"^\/+", "")

When a URI like //../../../../etc/passwd is passed: 1. get_template() strips all / → ../../../../etc/passwd → file found via posixpath.join(dir_, u) 2. Template.__init__ strips one / → /../../../../etc/passwd → normpath → /etc/passwd 3. /etc/passwd.startswith(..) → False → check bypassed

Impact

Arbitrary file read: any file readable by the process can be returned as rendered template content when an application passes untrusted input directly to TemplateLookup.get_template().

Note: this is exploitable at the library API level. HTTP-based exploitation is mitigated by Python's BaseHTTPRequestHandler which normalizes double-slash prefixes since CPython gh-87389. Applications using other HTTP servers that do not normalize paths may be affected.

Fix

Changed Template.__init__ to use lstrip("/") instead of stripping only a single leading slash, so both code paths handle leading slashes consistently.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
7.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mako",
        "resource_purl": "pkg:pypi/mako@1.4.1",
        "upstream_fixed_in": "1.3.11"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "core-lightning",
        "purl": "pkg:brew/core-lightning"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "26.06.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mako@1.4.1",
        "name": "mako",
        "resource": "mako",
        "strategy": "registry",
        "subject_version": "1.4.1"
      }
    ]
  },
  "details": "### Summary\n\n`TemplateLookup.get_template()` is vulnerable to path traversal when a URI starts with `//` (e.g., `//../../../secret.txt`). The root cause is an inconsistency between two slash-stripping implementations:\n\n- `Template.__init__` strips **one** leading `/` using `if`/slice\n- `TemplateLookup.get_template()` strips **all** leading `/` using `re.sub(r\"^\\/+\", \"\")`\n\nWhen a URI like `//../../../../etc/passwd` is passed:\n1. `get_template()` strips all `/` \u2192 `../../../../etc/passwd` \u2192 file found via `posixpath.join(dir_, u)`\n2. `Template.__init__` strips one `/` \u2192 `/../../../../etc/passwd` \u2192 `normpath` \u2192 `/etc/passwd`\n3. `/etc/passwd`.startswith(`..`) \u2192 `False` \u2192 **check bypassed**\n\n### Impact\n\nArbitrary file read: any file readable by the process can be returned as rendered template content when an application passes untrusted input directly to `TemplateLookup.get_template()`.\n\nNote: this is exploitable at the library API level. HTTP-based exploitation is mitigated by Python\u0027s `BaseHTTPRequestHandler` which normalizes double-slash prefixes since CPython gh-87389. Applications using other HTTP servers that do not normalize paths may be affected.\n\n### Fix\n\nChanged `Template.__init__` to use `lstrip(\"/\")` instead of stripping only a single leading slash, so both code paths handle leading slashes consistently.",
  "id": "BREW-core-lightning-CVE-2026-41205",
  "modified": "2026-09-12T08:48:34Z",
  "published": "2026-08-13T16:41:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/security/advisories/GHSA-v92g-xgxw-vvmm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41205"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/commit/e05ac61989a7fb9dd7dcde6cfd72dc48328719a3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pypa/advisory-database/tree/main/vulns/mako/PYSEC-2026-88.yaml"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sqlalchemy/mako"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sqlalchemy/mako/releases/tag/rel_1_3_11"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Mako: Path traversal via double-slash URI prefix in TemplateLookup",
  "upstream": [
    "GHSA-v92g-xgxw-vvmm",
    "CVE-2026-41205",
    "PYSEC-2026-88"
  ]
}



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