diff --git a/src/vouch/secrets.py b/src/vouch/secrets.py
index d6a5a832..d30dd22c 100644
--- a/src/vouch/secrets.py
+++ b/src/vouch/secrets.py
@@ -36,20 +36,37 @@
 _BEARER = re.compile(r"(?i)\b(Bearer)\s+[A-Za-z0-9._~+/=-]{10,}")
 
 # key=value / key: value for sensitive-looking names — mask the value, keep the
-# name so the redaction is legible.
+# name so the redaction is legible. Optional quote after the name covers JSON /
+# quoted-key shapes (`"password": "..."`). Quoted values are matched as a whole
+# unit (whitespace + escapes allowed) and their delimiters are preserved so the
+# redacted form stays structurally valid and cannot leak a trailing token.
 _ASSIGNMENT = re.compile(
     r"(?i)\b(api[_-]?key|secret|token|password|passwd|pwd|access[_-]?key)\b"
-    r"(\s*[:=]\s*)"
-    r"[\"']?[^\s\"']{6,}[\"']?"
+    r"([\"']?\s*[:=]\s*)"
+    r"(?:"
+    r"\"((?:\\.|[^\"\\]){6,})\""
+    r"|'((?:\\.|[^'\\]){6,})'"
+    r"|([^\s\"']{6,})"
+    r")"
 )
 
 
+def _redact_assignment(match: re.Match[str]) -> str:
+    """Keep key + separator; replace value, preserving quote delimiters."""
+    head = f"{match.group(1)}{match.group(2)}"
+    if match.group(3) is not None:
+        return f'{head}"{REDACTION}"'
+    if match.group(4) is not None:
+        return f"{head}'{REDACTION}'"
+    return f"{head}{REDACTION}"
+
+
 def mask_secrets(text: str) -> str:
     """Return ``text`` with detected secrets replaced by :data:`REDACTION`."""
     for pat in _SECRET_PATTERNS:
         text = pat.sub(REDACTION, text)
     text = _BEARER.sub(rf"\1 {REDACTION}", text)
-    text = _ASSIGNMENT.sub(rf"\1\2{REDACTION}", text)
+    text = _ASSIGNMENT.sub(_redact_assignment, text)
     return text
 
 
diff --git a/tests/test_secrets.py b/tests/test_secrets.py
index f293e108..f4be89e7 100644
--- a/tests/test_secrets.py
+++ b/tests/test_secrets.py
@@ -103,3 +103,32 @@ def test_cli_redact_command(tmp_path, monkeypatch) -> None:
     result = CliRunner().invoke(cli, ["redact", "c1"])
     assert result.exit_code == 0, result.output
     assert "ghp_" not in store.get_claim("c1").text
+
+
+def test_masks_json_quoted_key_credentials() -> None:
+    """JSON / quoted-key forms must not leak past the assignment mask (#549)."""
+    assert mask_secrets('"password": "hunter2secret"') == '"password": "[redacted-secret]"'
+    assert mask_secrets("'api_key': 'abcdefghij'") == "'api_key': '[redacted-secret]'"
+    assert mask_secrets('"token" : "abcdefghij"') == '"token" : "[redacted-secret]"'
+
+
+def test_masks_quoted_value_with_whitespace_and_escapes() -> None:
+    """Quoted values are whole units — whitespace must not leak a trailing token."""
+    text = '"password": "hunter2 secret"'
+    out = mask_secrets(text)
+    assert "hunter2 secret" not in out
+    assert "hunter2" not in out
+    assert out == '"password": "[redacted-secret]"'
+
+    # Value body includes escaped quotes: say \"hi\" nowxx
+    escaped = '"password": "say \\"hi\\" nowxx"'
+    assert '\\"hi\\"' in escaped
+    out2 = mask_secrets(escaped)
+    assert "nowxx" not in out2
+    assert out2 == '"password": "[redacted-secret]"'
+
+
+def test_masks_plain_assignment_still_works() -> None:
+    assert "hunter2secret" not in mask_secrets("password=hunter2secret")
+    assert "hunter2secret" not in mask_secrets("password: hunter2secret")
+    assert mask_secrets("password=hunter2secret") == "password=[redacted-secret]"