diff --git a/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.qhelp b/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.qhelp
new file mode 100644
index 000000000000..c731102849ef
--- /dev/null
+++ b/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.qhelp
@@ -0,0 +1,45 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+<overview>
+
+<p>Using the <code>"none"</code> algorithm when creating a JWT token with
+<code>JwtSecurityTokenHandler</code> disables signature verification. This allows attackers to
+forge arbitrary tokens that will be accepted as valid, potentially leading to authentication
+bypass and privilege escalation.</p>
+
+</overview>
+<recommendation>
+
+<p>Always use a secure signing algorithm such as <code>HS256</code>, <code>RS256</code>, or
+<code>ES256</code> when creating JWT tokens. Ensure that tokens are signed with a strong secret
+or key pair.</p>
+
+</recommendation>
+<example>
+
+<p>In this example, a JWT token is created using the <code>"none"</code> algorithm, which produces
+an unsigned token:</p>
+
+<sample src="examples/JwtNoneAlgorithmBad.ps1" />
+
+<p>The fix is to use a secure algorithm instead:</p>
+
+<sample src="examples/JwtNoneAlgorithmGood.ps1" />
+
+</example>
+<references>
+
+<li>
+RFC 7518:
+<a href="https://datatracker.ietf.org/doc/html/rfc7518#section-3.6">JSON Web Algorithms - Unsecured JWS</a>.
+</li>
+
+<li>
+CWE-347:
+<a href="https://cwe.mitre.org/data/definitions/347.html">Improper Verification of Cryptographic Signature</a>.
+</li>
+
+</references>
+</qhelp>
diff --git a/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.ql b/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.ql
new file mode 100644
index 000000000000..cfe282b828ba
--- /dev/null
+++ b/powershell/ql/src/queries/security/cwe-347/JwtNoneAlgorithm.ql
@@ -0,0 +1,37 @@
+/**
+ * @name JWT none algorithm usage
+ * @description Using the "none" algorithm for JWT tokens disables signature verification,
+ *              allowing token forgery.
+ * @kind problem
+ * @problem.severity error
+ * @security-severity 9.8
+ * @precision high
+ * @id powershell/jwt-none-algorithm
+ * @tags security
+ *       external/cwe/cwe-347
+ */
+
+import powershell
+import semmle.code.powershell.dataflow.DataFlow
+
+/**
+ * A string literal "none" passed as an algorithm argument to .NET JWT methods
+ * on a JwtSecurityTokenHandler instance.
+ */
+class JwtNoneInDotNetCall extends StringConstExpr {
+  JwtNoneInDotNetCall() {
+    this.getValueString().toLowerCase() = "none" and
+    exists(DataFlow::CallNode cn, DataFlow::ObjectCreationNode ocn |
+      cn.getQualifier().getALocalSource() = ocn and
+      ocn.getConstructedTypeNode().asExpr().getExpr().(TypeNameExpr).hasQualifiedName("system.identitymodel.tokens.jwt", "jwtsecuritytokenhandler") and
+      cn.getLowerCaseName() in [
+          "createtoken", "writetoken", "createjwtsecuritytoken", "createencodedjwt"
+        ] and
+      cn.getAnArgument().asExpr().getExpr() = this
+    )
+  }
+}
+
+from JwtNoneInDotNetCall noneAlg
+select noneAlg,
+  "JWT token created with 'none' algorithm via .NET API, disabling signature verification."
diff --git a/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmBad.ps1 b/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmBad.ps1
new file mode 100644
index 000000000000..535765c884d4
--- /dev/null
+++ b/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmBad.ps1
@@ -0,0 +1,4 @@
+$handler = [System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler]::new()
+
+# BAD: Creating a JWT token with the "none" algorithm disables signature verification.
+$token = $handler.CreateToken("none")
diff --git a/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmGood.ps1 b/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmGood.ps1
new file mode 100644
index 000000000000..77d39023cb1f
--- /dev/null
+++ b/powershell/ql/src/queries/security/cwe-347/examples/JwtNoneAlgorithmGood.ps1
@@ -0,0 +1,4 @@
+$handler = [System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler]::new()
+
+# GOOD: Creating a JWT token with a secure algorithm.
+$token = $handler.CreateToken("HS256")
diff --git a/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.expected b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.expected
new file mode 100644
index 000000000000..99a8061d7f1b
--- /dev/null
+++ b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.expected
@@ -0,0 +1,2 @@
+| test.ps1:7:31:7:36 | none | JWT token created with 'none' algorithm via .NET API, disabling signature verification. |
+| test.ps1:10:36:10:41 | none | JWT token created with 'none' algorithm via .NET API, disabling signature verification. |
diff --git a/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.qlref b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.qlref
new file mode 100644
index 000000000000..454d269bd3d2
--- /dev/null
+++ b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/JwtNoneAlgorithm.qlref
@@ -0,0 +1 @@
+queries/security/cwe-347/JwtNoneAlgorithm.ql
diff --git a/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/test.ps1 b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/test.ps1
new file mode 100644
index 000000000000..4be810003ab5
--- /dev/null
+++ b/powershell/ql/test/query-tests/security/cwe-347/JwtNoneAlgorithm/test.ps1
@@ -0,0 +1,17 @@
+# ===================================================================
+# ========== TRUE POSITIVES (should trigger alert) ==================
+# ===================================================================
+
+# --- Case 1: .NET JwtSecurityTokenHandler.CreateToken with "none" ---
+$handler = [System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler]::new()
+$token = $handler.CreateToken("none") # BAD
+
+# --- Case 2: .NET JwtSecurityTokenHandler.CreateEncodedJwt with "none" ---
+$token = $handler.CreateEncodedJwt("none") # BAD
+
+# ===================================================================
+# ========== TRUE NEGATIVES (should NOT trigger alert) ==============
+# ===================================================================
+
+# --- Safe: .NET CreateToken with HS256 ---
+$token = $handler.CreateToken("HS256") # GOOD