diff --git a/java/jtest/TestH5Affm.java b/java/jtest/TestH5Affm.java
index 96db05ec7e0..6afa6b33071 100644
--- a/java/jtest/TestH5Affm.java
+++ b/java/jtest/TestH5Affm.java
@@ -1027,7 +1027,7 @@ public class TestH5Affm {
     }
 
     @Test
-    public void testH5Aiterate()
+    public void testH5Aiterate_nullCallback()
     {
         System.out.print(testname.getMethodName());
 
@@ -1035,10 +1035,10 @@ public class TestH5Affm {
             MemorySegment idx = allocateLongArray(arena, 1);
             copyToSegment(idx, new long[] {0});
 
-            // Just verify the API works, iteration callback complex for FFM
+            // NULL callback must be rejected gracefully (H5E_BADVALUE), not crash
             long result = hdf5_h.H5Aiterate2(H5did, hdf5_h.H5_INDEX_NAME(), hdf5_h.H5_ITER_INC(), idx,
                                              MemorySegment.NULL, MemorySegment.NULL);
-            assertTrue("H5Aiterate2 should complete", result >= 0);
+            assertTrue("H5Aiterate2 should fail when callback is NULL", result < 0);
         }
     }
 }
diff --git a/release_docs/CHANGELOG.md b/release_docs/CHANGELOG.md
index ac8ce4e95c0..30113c2ddee 100644
--- a/release_docs/CHANGELOG.md
+++ b/release_docs/CHANGELOG.md
@@ -155,6 +155,12 @@ The `h5repack` tool now obtains its default low and high library version bounds
 
    Previously the error stack would be cleared when exiting a data filter, even an internal library filter, so the user could not see what caused the filter to fail. This has been fixed by not treating internal data filters like a user callback. Note that user-defined or third-party filters that use the default error stack will need to print that stack before returning from their callbacks.
 
+### Fixed error when reading variable-length chunked datasets in read-only mode
+
+   Passing NULL for the callback function pointer to H5Aiterate2 and H5Aiterate_by_name was not detected, leading to a subsequent access of an uninitialized pointer. This is now fixed.
+
+    Fixes CVE-2025-9274
+
 ### Fixed error when reading variable-length chunked datasets in read-only mode
 
    When reading from a chunked dataset with a variable-length type, a non-default fill value, and unwritten chunks, the library would internally try to write data to the file and fail due to writing to a read-only file. Reworked the I/O code to avoid these writes in this case. This may also improve performance and file space usage in similar cases with files open with write access.
diff --git a/src/H5A.c b/src/H5A.c
index 9d4862d327b..028e473f107 100644
--- a/src/H5A.c
+++ b/src/H5A.c
@@ -1869,6 +1869,8 @@ H5Aiterate2(hid_t loc_id, H5_index_t idx_type, H5_iter_order_t order, hsize_t *i
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid index type specified");
     if (order <= H5_ITER_UNKNOWN || order >= H5_ITER_N)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid iteration order specified");
+    if (op == NULL)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no operator specified");
 
     /* Get the loc object */
     if (NULL == (vol_obj = H5VL_vol_object(loc_id)))
@@ -1958,6 +1960,8 @@ H5Aiterate_by_name(hid_t loc_id, const char *obj_name, H5_index_t idx_type, H5_i
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid index type specified");
     if (order <= H5_ITER_UNKNOWN || order >= H5_ITER_N)
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "invalid iteration order specified");
+    if (op == NULL)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "no operator specified");
 
     /* Verify access property list and set up collective metadata if appropriate */
     if (H5CX_set_apl(&lapl_id, H5P_CLS_LACC, loc_id, false) < 0)
diff --git a/test/tattr.c b/test/tattr.c
index af08d2db0a2..126d61e0e0d 100644
--- a/test/tattr.c
+++ b/test/tattr.c
@@ -7608,6 +7608,14 @@ attr_iterate_check(hid_t fid, const char *dsetname, hid_t obj_id, H5_index_t idx
     H5E_END_TRY
     VERIFY(ret, FAIL, "H5Aiterate_by_name");
 
+    /* Test passing null pointer for callback */
+    H5E_BEGIN_TRY
+    {
+        ret = H5Aiterate_by_name(obj_id, ".", idx_type, order, &skip, NULL, NULL, H5P_DEFAULT);
+    }
+    H5E_END_TRY
+    VERIFY(ret, FAIL, "H5Aiterate_by_name");
+
     /* Retrieve current # of errors */
     if (old_nerrs == GetTestNumErrs())
         return (0);
diff --git a/test/titerate.c b/test/titerate.c
index 595a577d8f6..ab448cc7b87 100644
--- a/test/titerate.c
+++ b/test/titerate.c
@@ -539,6 +539,14 @@ test_iter_attr(hid_t fapl, bool new_format)
     H5E_END_TRY
     VERIFY(ret, FAIL, "H5Aiterate2");
 
+    /* Test passing null pointer for callback */
+    H5E_BEGIN_TRY
+    {
+        ret = H5Aiterate2(dataset, H5_INDEX_NAME, H5_ITER_INC, &idx, NULL, &info);
+    }
+    H5E_END_TRY
+    VERIFY(ret, FAIL, "H5Aiterate2");
+
     /* Test all attributes on dataset, when callback always returns 0 */
     info.command = RET_ZERO;
     idx          = 0;