CVE-2025-48990: NeKernel Buffer Overflow Vulnerability

CVE-2025-48990 Overview

CVE-2025-48990 is a 1-byte heap overflow in NeKernal version 0.0.2, an open-source operating system stack. The flaw resides in the rt_copy_memory utility function, which unconditionally writes a null terminator at dst[len] after copying. When len equals the size of the destination buffer (256 bytes), this terminator write overruns the allocation by one byte. The issue is tracked as [CWE-122: Heap-based Buffer Overflow] and was addressed in commit fb7b7f658327f659c6a6da1af151cb389c2ca4ee.

Critical Impact
A local attacker who can influence input passed into rt_copy_memory may corrupt adjacent heap metadata, leading to memory corruption and potential code execution within the kernel context.

Affected Products

NeKernal 0.0.2
dev/kernel/src/Utils.cc — rt_copy_memory routine
Builds prior to commit fb7b7f658327f659c6a6da1af151cb389c2ca4ee

Discovery Timeline

2025-06-02 - CVE-2025-48990 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-48990

Vulnerability Analysis

The defect is an off-by-one heap overflow caused by an unconditional null terminator write. rt_copy_memory copies len bytes from a source into a heap-allocated destination buffer, then writes dstChar[index] = 0; at the byte immediately following the last copied byte. When the caller passes a len value equal to the buffer's allocated size (256 bytes in the documented case), the terminator is written one byte past the end of the allocation.

This single byte overflow can corrupt adjacent heap metadata or neighboring object data. In kernel-mode allocators, even single-byte overflows are exploitable primitives because they can modify allocator chunk headers, free-list pointers, or object type tags. The bug class is well-documented under CWE-122.

Root Cause

The root cause is a missing relationship between the len parameter and the destination buffer size. The function treats the destination as if it always has room for len + 1 bytes, but callers allocate exactly len bytes. No bounds check exists between the copy loop and the terminator write.

Attack Vector

Exploitation requires local access and the ability to invoke a code path that calls rt_copy_memory with attacker-controlled length or content that fills the destination buffer exactly. Because the function operates in kernel context, successful corruption of adjacent heap structures can escalate to arbitrary kernel memory writes.

text

// Patch hunk from dev/kernel/src/Utils.cc
     ++index;
   }
 
-  dstChar[index] = 0;
-
   return index;
 }

Source: GitHub commit fb7b7f6. The fix removes the overflow-causing terminator write entirely, preserving the public API and avoiding changes to existing callers.

Detection Methods for CVE-2025-48990

Indicators of Compromise

Unexpected kernel panics or heap allocator assertions originating from code paths that call rt_copy_memory.
Heap corruption diagnostics flagging single-byte overwrites adjacent to 256-byte allocations.
Builds of NeKernal that include dev/kernel/src/Utils.cc without commit fb7b7f658327f659c6a6da1af151cb389c2ca4ee applied.

Detection Strategies

Run NeKernal builds under sanitizers such as AddressSanitizer or KASAN to catch the off-by-one write at runtime.
Perform static analysis on rt_copy_memory callers to identify invocations where len may equal the destination buffer size.
Audit version control metadata of deployed NeKernal images to confirm the fix commit is included.

Monitoring Recommendations

Track NeKernal upstream commits and the GHSA-jvvh-fp57-2p32 advisory for updates.
Log kernel allocator faults and segmentation events from NeKernal test environments to detect exploitation attempts.

How to Mitigate CVE-2025-48990

Immediate Actions Required

Rebuild NeKernel from a source tree that includes commit fb7b7f658327f659c6a6da1af151cb389c2ca4ee.
Restrict local access to systems running unpatched NeKernal 0.0.2 builds until the fix is deployed.
Audit downstream forks for an independent copy of the vulnerable rt_copy_memory implementation.

Patch Information

The maintainers shipped a minimal fix in commit fb7b7f6 that removes the line dstChar[index] = 0; from rt_copy_memory. The patch deliberately avoids adding bounds checks or modifying the public API to prevent regressions in existing callers. Details are also published in GitHub Security Advisory GHSA-jvvh-fp57-2p32.

Workarounds

Callers that rely on null termination must allocate len + 1 bytes for the destination and terminate the buffer themselves after invoking rt_copy_memory.
Limit len arguments to at most sizeof(dst) - 1 in caller code paths that cannot be rebuilt immediately.

bash

# Apply the upstream fix
git clone https://github.com/nekernel-org/nekernel.git
cd nekernel
git checkout fb7b7f658327f659c6a6da1af151cb389c2ca4ee
# Rebuild the kernel according to project instructions