Python: Model new binascii codecs

python/ql/lib/change-notes/2026-09-22-python315-binascii.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Added modeling for the Base32, Base85, and Ascii85 encoding and decoding functions introduced in Python 3.15's `binascii` module, including taint flow through custom alphabets.

python/ql/lib/semmle/python/frameworks/Stdlib.qll

@@ -1760,6 +1760,59 @@ module StdlibPrivate {
     }
   }
 
+  // ---------------------------------------------------------------------------
+  // binascii
+  // ---------------------------------------------------------------------------
+  /** A call to a supported encoding function in the `binascii` module. */
+  private class BinasciiEncodeCall extends Encoding::Range, DataFlow::CallCfgNode {
+    string codec;
+
+    BinasciiEncodeCall() {
+      codec in ["base32", "base85", "ascii85"] and
+      this = API::moduleImport("binascii").getMember("b2a_" + codec).getACall()
+    }
+
+    override DataFlow::Node getAnInput() {
+      result = this.getArg(0)
+      or
+      codec in ["base32", "base85"] and
+      result = this.getArgByName("alphabet")
+    }
+
+    override DataFlow::Node getOutput() { result = this }
+
+    override string getFormat() {
+      result in ["Base32", "Base85", "Ascii85"] and
+      result.toLowerCase() = codec
+    }
+  }
+
+  /** A call to a supported decoding function in the `binascii` module. */
+  private class BinasciiDecodeCall extends Decoding::Range, DataFlow::CallCfgNode {
+    string codec;
+
+    BinasciiDecodeCall() {
+      codec in ["base32", "base85", "ascii85"] and
+      this = API::moduleImport("binascii").getMember("a2b_" + codec).getACall()
+    }
+
+    override predicate mayExecuteInput() { none() }
+
+    override DataFlow::Node getAnInput() {
+      result = this.getArg(0)
+      or
+      codec in ["base32", "base85"] and
+      result = this.getArgByName("alphabet")
+    }
+
+    override DataFlow::Node getOutput() { result = this }
+
+    override string getFormat() {
+      result in ["Base32", "Base85", "Ascii85"] and
+      result.toLowerCase() = codec
+    }
+  }
+
   // ---------------------------------------------------------------------------
   // json
   // ---------------------------------------------------------------------------

python/ql/test/library-tests/frameworks/stdlib/test_binascii.py

@@ -0,0 +1,72 @@
+import binascii
+from binascii import b2a_base32 as encode32, a2b_base85 as decode85
+
+data = TAINTED_BYTES
+
+encoded32 = binascii.b2a_base32(data, padded=False) # $ encodeInput=data encodeOutput=binascii.b2a_base32(..) encodeFormat=Base32
+decoded32 = binascii.a2b_base32(encoded32, padded=False, canonical=True) # $ decodeInput=encoded32 decodeOutput=binascii.a2b_base32(..) decodeFormat=Base32
+
+encoded85 = binascii.b2a_base85(data, pad=True) # $ encodeInput=data encodeOutput=binascii.b2a_base85(..) encodeFormat=Base85
+decoded85 = binascii.a2b_base85(encoded85, canonical=True) # $ decodeInput=encoded85 decodeOutput=binascii.a2b_base85(..) decodeFormat=Base85
+
+encoded_ascii85 = binascii.b2a_ascii85(data, foldspaces=True, adobe=True) # $ encodeInput=data encodeOutput=binascii.b2a_ascii85(..) encodeFormat=Ascii85
+decoded_ascii85 = binascii.a2b_ascii85(encoded_ascii85, foldspaces=True, adobe=True) # $ decodeInput=encoded_ascii85 decodeOutput=binascii.a2b_ascii85(..) decodeFormat=Ascii85
+
+ensure_tainted(
+    encoded32, # $ tainted
+    decoded32, # $ tainted
+    encoded85, # $ tainted
+    decoded85, # $ tainted
+    encoded_ascii85, # $ tainted
+    decoded_ascii85, # $ tainted
+)
+
+aliased_encoded = encode32(data) # $ encodeInput=data encodeOutput=encode32(..) encodeFormat=Base32
+aliased_decoded = decode85(encoded85) # $ decodeInput=encoded85 decodeOutput=decode85(..) decodeFormat=Base85
+ensure_tainted(
+    aliased_encoded, # $ tainted
+    aliased_decoded, # $ tainted
+)
+
+
+def custom_alphabets():
+    alphabet32 = binascii.BASE32HEX_ALPHABET
+    alphabet85 = binascii.Z85_ALPHABET
+    taint(alphabet32, alphabet85)
+
+    clean = b"abcd"
+    clean32 = b"00000000"
+    clean85 = b"00000"
+    encoded32 = binascii.b2a_base32(clean, alphabet=alphabet32) # $ encodeInput=clean encodeInput=alphabet32 encodeOutput=binascii.b2a_base32(..) encodeFormat=Base32
+    decoded32 = binascii.a2b_base32(clean32, alphabet=alphabet32) # $ decodeInput=clean32 decodeInput=alphabet32 decodeOutput=binascii.a2b_base32(..) decodeFormat=Base32
+    encoded85 = binascii.b2a_base85(clean, alphabet=alphabet85) # $ encodeInput=clean encodeInput=alphabet85 encodeOutput=binascii.b2a_base85(..) encodeFormat=Base85
+    decoded85 = binascii.a2b_base85(clean85, alphabet=alphabet85) # $ decodeInput=clean85 decodeInput=alphabet85 decodeOutput=binascii.a2b_base85(..) decodeFormat=Base85
+    ensure_tainted(
+        encoded32, # $ tainted
+        decoded32, # $ tainted
+        encoded85, # $ tainted
+        decoded85, # $ tainted
+    )
+
+
+def clean_inputs():
+    clean = b"abcd"
+    empty = b""
+    wrapcol = 80
+    ignorechars = b" \n"
+    taint(wrapcol, ignorechars)
+
+    encoded32 = binascii.b2a_base32(clean, wrapcol=wrapcol) # $ encodeInput=clean encodeOutput=binascii.b2a_base32(..) encodeFormat=Base32
+    encoded85 = binascii.b2a_base85(clean, wrapcol=wrapcol) # $ encodeInput=clean encodeOutput=binascii.b2a_base85(..) encodeFormat=Base85
+    encoded_ascii85 = binascii.b2a_ascii85(clean, wrapcol=wrapcol) # $ encodeInput=clean encodeOutput=binascii.b2a_ascii85(..) encodeFormat=Ascii85
+    decoded32 = binascii.a2b_base32(empty, ignorechars=ignorechars) # $ decodeInput=empty decodeOutput=binascii.a2b_base32(..) decodeFormat=Base32
+    decoded85 = binascii.a2b_base85(empty, ignorechars=ignorechars) # $ decodeInput=empty decodeOutput=binascii.a2b_base85(..) decodeFormat=Base85
+    decoded_ascii85 = binascii.a2b_ascii85(empty, ignorechars=ignorechars) # $ decodeInput=empty decodeOutput=binascii.a2b_ascii85(..) decodeFormat=Ascii85
+    ensure_not_tainted(
+        encoded32,
+        encoded85,
+        encoded_ascii85,
+        decoded32,
+        decoded85,
+        decoded_ascii85,
+    )