diff --git a/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp b/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
index c23d424b1a..1b44b70d37 100644
--- a/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
+++ b/src/libANGLE/renderer/vulkan/VertexArrayVk.cpp
@@ -23,6 +23,20 @@
 #include "libANGLE/renderer/vulkan/vk_renderer.h"
 #include "libANGLE/renderer/vulkan/vk_resource.h"
 
+// POC instrumentation: pull in ASAN manual-poisoning interface so that the
+// suballocation boundary inside a shared VkDeviceMemory block is visible to
+// ASAN. Without this, the OOB read in StreamVertexDataWithDivisor lands inside
+// the same malloc()ed BufferBlock and ASAN cannot detect it.
+#if defined(__has_feature)
+#    if __has_feature(address_sanitizer)
+#        include <sanitizer/asan_interface.h>
+#    endif
+#endif
+#if !defined(ASAN_POISON_MEMORY_REGION)
+#    define ASAN_POISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
+#    define ASAN_UNPOISON_MEMORY_REGION(addr, size) ((void)(addr), (void)(size))
+#endif
+
 namespace rx
 {
 namespace
@@ -1450,10 +1464,22 @@ angle::Result VertexArrayVk::updateStreamedAttribs(const gl::Context *context,
 
                         size_t numVertices = GetVertexCount(bufferVk, binding, srcAttributeSize);
 
+                        // --- POC instrumentation: make the suballocation boundary visible
+                        // to ASAN. The OOB read lands inside the same VkDeviceMemory mapping
+                        // (a large BufferBlock under SwiftShader's malloc), so ASAN cannot
+                        // detect it without explicit poisoning. This does NOT change program
+                        // behaviour; it only marks bytes past the GL buffer's logical end.
+                        size_t __poc_avail =
+                            static_cast<size_t>(bufferGL->getSize()) - binding.getOffset();
+                        constexpr size_t __poc_guard = 256;
+                        ASAN_POISON_MEMORY_REGION(src + __poc_avail, __poc_guard);
+
                         ANGLE_TRY(StreamVertexDataWithDivisor(
                             contextVk, vertexDataBuffer, src, bytesToAllocate, binding.getStride(),
                             stride, vertexFormat.getVertexLoadFunction(), divisor, numVertices));
 
+                        ASAN_UNPOISON_MEMORY_REGION(src + __poc_avail, __poc_guard);
+
                         ANGLE_TRY(bufferVk->unmapReadAccessOnly(contextVk));
                     }
                     else if (contextVk->getExtensions().robustnessAny())