From eb5017870dd6c96c1994a1b94150237e68edb179 Mon Sep 17 00:00:00 2001
From: Florence Blanc-Renaud <flo@redhat.com>
Date: Thu, 12 Feb 2026 23:18:56 +0100
Subject: [PATCH] Backport commit be353d7

Add limit of 20 continuation octets per OID arc to prevent a potential memory
exhaustion from excessive continuation bytes input.
---
 pyasn1/codec/ber/decoder.py     | 11 ++++++
 tests/codec/ber/test_decoder.py | 66 +++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+)

diff --git a/pyasn1/codec/ber/decoder.py b/pyasn1/codec/ber/decoder.py
index 5ff485fbeb0cc7d761dd398134cf39a6258a109e..adfd7501a52421748b3143935a0ec95bdd1d42e6 100644
--- a/pyasn1/codec/ber/decoder.py
+++ b/pyasn1/codec/ber/decoder.py
@@ -22,6 +22,10 @@ LOG = debug.registerLoggee(__name__, flags=debug.DEBUG_DECODER)
 
 noValue = base.noValue
 
+# Maximum number of continuation octets (high-bit set) allowed per OID arc.
+# 20 octets allows up to 140-bit integers, supporting UUID-based OIDs
+MAX_OID_ARC_CONTINUATION_OCTETS = 20
+
 
 class AbstractDecoder(object):
     protoComponent = None
@@ -342,7 +346,14 @@ class ObjectIdentifierDecoder(AbstractSimpleDecoder):
                 # Construct subid from a number of octets
                 nextSubId = subId
                 subId = 0
+                continuationOctetCount = 0
                 while nextSubId >= 128:
+                    continuationOctetCount += 1
+                    if continuationOctetCount > MAX_OID_ARC_CONTINUATION_OCTETS:
+                        raise error.PyAsn1Error(
+                            'OID arc exceeds maximum continuation octets limit (%d) '
+                            'at position %d' % (MAX_OID_ARC_CONTINUATION_OCTETS, index)
+                        )
                     subId = (subId << 7) + (nextSubId & 0x7F)
                     if index >= substrateLen:
                         raise error.SubstrateUnderrunError(
diff --git a/tests/codec/ber/test_decoder.py b/tests/codec/ber/test_decoder.py
index e3b74dfd203923157cb6a26215e9d03c971a5b41..f9bf381b1da339611d974673420248e1a1014421 100644
--- a/tests/codec/ber/test_decoder.py
+++ b/tests/codec/ber/test_decoder.py
@@ -407,6 +407,72 @@ class ObjectIdentifierDecoderTestCase(BaseTestCase):
             ints2octs((0x06, 0x13, 0x88, 0x37, 0x83, 0xC6, 0xDF, 0xD4, 0xCC, 0xB3, 0xFF, 0xFF, 0xFE, 0xF0, 0xB8, 0xD6, 0xB8, 0xCB, 0xE2, 0xB6, 0x47))
         ) == ((2, 999, 18446744073709551535184467440737095), null)
 
+    def testExcessiveContinuationOctets(self):
+        """Test that OID arcs with excessive continuation octets are rejected."""
+        # Create a payload with 25 continuation octets (exceeds 20 limit)
+        # 0x81 bytes are continuation octets, 0x01 terminates
+        malicious_payload = bytes([0x06, 26]) + bytes([0x81] * 25) + bytes([0x01])
+        try:
+            decoder.decode(malicious_payload)
+        except PyAsn1Error:
+            pass
+        else:
+            assert 0, 'Excessive continuation octets tolerated'
+
+    def testMaxAllowedContinuationOctets(self):
+        """Test that OID arcs at the maximum continuation octets limit work."""
+        # Create a payload with exactly 20 continuation octets (at limit)
+        # This should succeed
+        payload = bytes([0x06, 21]) + bytes([0x81] * 20) + bytes([0x01])
+        try:
+            decoder.decode(payload)
+        except PyAsn1Error:
+            assert 0, 'Valid OID with 20 continuation octets rejected'
+
+    def testOneOverContinuationLimit(self):
+        """Test boundary: 21 continuation octets (one over limit) is rejected."""
+        payload = bytes([0x06, 22]) + bytes([0x81] * 21) + bytes([0x01])
+        try:
+            decoder.decode(payload)
+        except PyAsn1Error:
+            pass
+        else:
+            assert 0, '21 continuation octets tolerated (should be rejected)'
+
+    def testExcessiveContinuationInSecondArc(self):
+        """Test that limit applies to subsequent arcs, not just the first."""
+        # First arc: valid simple byte (0x55 = 85, decodes to arc 2.5)
+        # Second arc: excessive continuation octets
+        payload = bytes([0x06, 27]) + bytes([0x55]) + bytes([0x81] * 25) + bytes([0x01])
+        try:
+            decoder.decode(payload)
+        except PyAsn1Error:
+            pass
+        else:
+            assert 0, 'Excessive continuation in second arc tolerated'
+
+    def testMultipleArcsAtLimit(self):
+        """Test multiple arcs each at the continuation limit work correctly."""
+        # Two arcs, each with 20 continuation octets (both at limit)
+        arc1 = bytes([0x81] * 20) + bytes([0x01])  # 21 bytes
+        arc2 = bytes([0x81] * 20) + bytes([0x01])  # 21 bytes
+        payload = bytes([0x06, 42]) + arc1 + arc2
+        try:
+            decoder.decode(payload)
+        except PyAsn1Error:
+            assert 0, 'Multiple valid arcs at limit rejected'
+
+    def testExcessiveContinuationWithMaxBytes(self):
+        """Test with 0xFF continuation bytes (maximum value, not just 0x81)."""
+        # 0xFF bytes are also continuation octets (high bit set)
+        malicious_payload = bytes([0x06, 26]) + bytes([0xFF] * 25) + bytes([0x01])
+        try:
+            decoder.decode(malicious_payload)
+        except PyAsn1Error:
+            pass
+        else:
+            assert 0, 'Excessive 0xFF continuation octets tolerated'
+
 
 class RealDecoderTestCase(BaseTestCase):
     def testChar(self):
-- 
2.52.0