fix(java): match mixed-case weak crypto algorithm strings

Author: sam-robson

java/ql/lib/change-notes/2026-11-05-weak-crypto-case-sensitivity.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `java/weak-cryptographic-algorithm` and `java/potentially-weak-cryptographic-algorithm` queries now match cryptographic algorithm names and modes case-insensitively (for example, `AES/CBC/PKCS5PADDING` and `AES/cbc/Pkcs5Padding`).

java/ql/lib/semmle/code/java/security/BrokenCryptoAlgorithmQuery.qll

@@ -17,7 +17,7 @@ class BrokenAlgoLiteral extends ShortStringLiteral {
   BrokenAlgoLiteral() {
     this.getValue().regexpMatch(getInsecureAlgorithmRegex()) and
     // Exclude RSA/ECB/.* ciphers.
-    not this.getValue().regexpMatch("RSA/ECB.*") and
+    not this.getValue().regexpMatch("(?i)RSA/ECB.*") and
     // Exclude German and French sentences.
     not this.getValue().regexpMatch(".*\\p{IsLowercase} des \\p{IsLetter}.*")
   }

java/ql/lib/semmle/code/java/security/Encryption.qll

@@ -189,15 +189,18 @@ bindingset[algorithmString]
 private string algorithmRegex(string algorithmString) {
   // Algorithms usually appear in names surrounded by characters that are not
   // alphabetical characters in the same case. This handles the upper and lower
-  // case cases.
+  // case cases, plus mixed-case algorithm strings bounded by non-alphabetic
+  // characters (such as `AES/cbc/Pkcs5Padding`).
   result =
     "((^|.*[^A-Z])(" + algorithmString + ")([^A-Z].*|$))" +
       // or...
       "|" +
       // For lowercase, we want to be careful to avoid being confused by camelCase
       // hence we require two preceding uppercase letters to be sure of a case switch,
       // or a preceding non-alphabetic character
-      "((^|.*[A-Z]{2}|.*[^a-zA-Z])(" + algorithmString.toLowerCase() + ")([^a-z].*|$))"
+      "((^|.*[A-Z]{2}|.*[^a-zA-Z])(" + algorithmString.toLowerCase() + ")([^a-z].*|$))" +
+      // or...
+      "|" + "((^|.*[^a-zA-Z])(?i)(" + algorithmString + ")([^a-zA-Z].*|$))"
 }
 
 /**
@@ -258,7 +261,7 @@ string getInsecureAlgorithmReason(string input) {
 string getASecureAlgorithmName() {
   result =
     [
-      "RSA", "SHA-?(256|384|512)", "CCM", "GCM", "AES(?![^a-zA-Z](ECB|CBC/PKCS[57]Padding))",
+      "RSA", "SHA-?(256|384|512)", "CCM", "GCM", "AES(?![^a-zA-Z](?i)(ECB|CBC/PKCS[57]Padding))",
       "Blowfish", "ECIES", "SHA3-(256|384|512)",
       // Elliptic Curve algorithms: EC (key generation), ECDSA (signatures), ECDH (key agreement),
       // EdDSA/Ed25519/Ed448 (Edwards-curve signatures), XDH/X25519/X448 (key agreement).

java/ql/test/query-tests/security/CWE-327/semmle/tests/BrokenCryptoAlgorithm.expected

@@ -1,8 +1,16 @@
 #select
 | Test.java:19:20:19:50 | getInstance(...) | Test.java:19:45:19:49 | "DES" | Test.java:19:45:19:49 | "DES" | Cryptographic algorithm $@ is insecure. It has a short key length of 56 bits, making it vulnerable to brute-force attacks. Consider using AES instead. | Test.java:19:45:19:49 | "DES" | DES |
 | Test.java:42:14:42:38 | getInstance(...) | Test.java:42:33:42:37 | "RC2" | Test.java:42:33:42:37 | "RC2" | Cryptographic algorithm $@ is insecure. It is vulnerable to related-key attacks. Consider using AES instead. | Test.java:42:33:42:37 | "RC2" | RC2 |
+| Test.java:46:14:46:55 | getInstance(...) | Test.java:46:33:46:54 | "AES/CBC/PKCS5Padding" | Test.java:46:33:46:54 | "AES/CBC/PKCS5Padding" | Cryptographic algorithm $@ is insecure. CBC mode with PKCS#5 or PKCS#7 padding is vulnerable to padding oracle attacks. Consider using GCM instead. | Test.java:46:33:46:54 | "AES/CBC/PKCS5Padding" | AES/CBC/PKCS5Padding |
+| Test.java:47:14:47:55 | getInstance(...) | Test.java:47:33:47:54 | "AES/CBC/PKCS5PADDING" | Test.java:47:33:47:54 | "AES/CBC/PKCS5PADDING" | Cryptographic algorithm $@ is insecure. CBC mode with PKCS#5 or PKCS#7 padding is vulnerable to padding oracle attacks. Consider using GCM instead. | Test.java:47:33:47:54 | "AES/CBC/PKCS5PADDING" | AES/CBC/PKCS5PADDING |
+| Test.java:48:14:48:55 | getInstance(...) | Test.java:48:33:48:54 | "aes/cbc/pkcs5padding" | Test.java:48:33:48:54 | "aes/cbc/pkcs5padding" | Cryptographic algorithm $@ is insecure. CBC mode with PKCS#5 or PKCS#7 padding is vulnerable to padding oracle attacks. Consider using GCM instead. | Test.java:48:33:48:54 | "aes/cbc/pkcs5padding" | aes/cbc/pkcs5padding |
+| Test.java:49:14:49:55 | getInstance(...) | Test.java:49:33:49:54 | "AES/cbc/Pkcs5Padding" | Test.java:49:33:49:54 | "AES/cbc/Pkcs5Padding" | Cryptographic algorithm $@ is insecure. CBC mode with PKCS#5 or PKCS#7 padding is vulnerable to padding oracle attacks. Consider using GCM instead. | Test.java:49:33:49:54 | "AES/cbc/Pkcs5Padding" | AES/cbc/Pkcs5Padding |
 edges
 nodes
 | Test.java:19:45:19:49 | "DES" | semmle.label | "DES" |
 | Test.java:42:33:42:37 | "RC2" | semmle.label | "RC2" |
+| Test.java:46:33:46:54 | "AES/CBC/PKCS5Padding" | semmle.label | "AES/CBC/PKCS5Padding" |
+| Test.java:47:33:47:54 | "AES/CBC/PKCS5PADDING" | semmle.label | "AES/CBC/PKCS5PADDING" |
+| Test.java:48:33:48:54 | "aes/cbc/pkcs5padding" | semmle.label | "aes/cbc/pkcs5padding" |
+| Test.java:49:33:49:54 | "AES/cbc/Pkcs5Padding" | semmle.label | "AES/cbc/Pkcs5Padding" |
 subpaths

java/ql/test/query-tests/security/CWE-327/semmle/tests/Test.java

@@ -41,6 +41,13 @@ public void test() {
 				// BAD: RC2 is a weak algorithm
 				cipher = Cipher.getInstance("RC2"); // $ Alert[java/weak-cryptographic-algorithm]
 			}
+			{
+				// BAD: AES/CBC/PKCS5Padding is vulnerable to padding oracle attacks, regardless of case
+				cipher = Cipher.getInstance("AES/CBC/PKCS5Padding"); // $ Alert[java/weak-cryptographic-algorithm]
+				cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING"); // $ Alert[java/weak-cryptographic-algorithm]
+				cipher = Cipher.getInstance("aes/cbc/pkcs5padding"); // $ Alert[java/weak-cryptographic-algorithm]
+				cipher = Cipher.getInstance("AES/cbc/Pkcs5Padding"); // $ Alert[java/weak-cryptographic-algorithm]
+			}
 			// GOOD: ECIES is a strong algorithm
 			cipher = Cipher.getInstance("ECIES");
 			cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec);