(pdfbox-jbig2) branch master updated: PDFBOX-6162: Fix IAID decoding by masking context index to lower N bits and preventing integer overflow in shifts

[msahyoun]

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asf-gitbox-commits pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/pdfbox-jbig2.git


The following commit(s) were added to refs/heads/master by this push:
     new eeea7fb  PDFBOX-6162: Fix IAID decoding by masking context index to 
lower N bits and preventing integer overflow in shifts
eeea7fb is described below

commit eeea7fb822223253c6eba8f96c1e4752540f5ed0
Author: Maruan Sahyoun <sahy...@fileaffairs.de>
AuthorDate: Tue Apr 21 11:02:00 2026 +0200

    PDFBOX-6162: Fix IAID decoding by masking context index to lower N bits and 
preventing integer overflow in shifts
---
 .../jbig2/decoder/arithmetic/ArithmeticIntegerDecoder.java | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git 
a/src/main/java/org/apache/pdfbox/jbig2/decoder/arithmetic/ArithmeticIntegerDecoder.java
 
b/src/main/java/org/apache/pdfbox/jbig2/decoder/arithmetic/ArithmeticIntegerDecoder.java
index 8ef9b56..5ba42c3 100644
--- 
a/src/main/java/org/apache/pdfbox/jbig2/decoder/arithmetic/ArithmeticIntegerDecoder.java
+++ 
b/src/main/java/org/apache/pdfbox/jbig2/decoder/arithmetic/ArithmeticIntegerDecoder.java
@@ -170,16 +170,24 @@ public class ArithmeticIntegerDecoder
     public int decodeIAID(CX cxIAID, long symCodeLen) throws IOException
     {
         // A.3 1)
-        prev = 1;
+        long prev = 1;
+
 
         // A.3 2)
+        // The spec says: "the rightmost SBSYMCODELEN + 1 bits of PREV are 
used"
+        // But also: "The number of contexts required is 2^SBSYMCODELEN"
+        // The resolution: the leading 1 bit is not used for context
+        // identification—only the lower N bits are.
+
+        long mask = (1L << symCodeLen) - 1;
+        
         for (int i = 0; i < symCodeLen; i++)
         {
-            cxIAID.setIndex(prev);
+            cxIAID.setIndex((int) (prev & mask));
             prev = (prev << 1) | decoder.decode(cxIAID);
         }
 
         // A.3 3) & 4)
-        return (prev - (1 << symCodeLen));
+        return (int) (prev - (1L << symCodeLen));
     }
 }