CVE-2025-51679 Overview
CVE-2025-51679 affects the openRISC OR1200 processor implementation at commit 83ac6b. A mismatch between the Register Transfer Level (RTL) description and the synthesized netlist can lead to unexpected hardware behavior. The issue was documented through an open-source hardware fuzzing research effort tracked in the Synfuzz project and referenced in a corresponding academic paper.
Because OR1200 is a soft-core CPU distributed as source, downstream projects that synthesize the affected commit can inherit divergent post-synthesis behavior. The full security impact depends on how integrators use the core.
Critical Impact
An RTL-to-netlist mismatch in the OR1200 core can produce hardware behavior that diverges from the design specification, undermining assumptions made by software running on the synthesized processor.
Affected Products
- openRISC OR1200 soft-core CPU at commit 83ac6b
- Downstream FPGA or ASIC designs integrating the affected OR1200 commit
- Simulation and verification environments relying on the divergent RTL
Discovery Timeline
- 2026-08-26 - CVE-2025-51679 published to the National Vulnerability Database (NVD)
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2025-51679
Vulnerability Analysis
The openRISC OR1200 is an open-source implementation of the OpenRISC 1000 32-bit CPU architecture. The reported issue is a mismatch between the RTL source and the netlist produced after synthesis. In digital hardware design, the RTL describes intended behavior, and the netlist represents the gate-level implementation used for fabrication or FPGA loading. Any divergence between these two representations means that verification performed on the RTL does not fully reflect what executes on hardware.
The root problem was surfaced by hardware fuzzing techniques applied to open-source cores, as documented in the referenced ArXiv research paper and the Synfuzz CVE list. See the upstream openRISC issue tracker entry for the maintainer discussion.
Root Cause
The root cause is a synthesis-related discrepancy. Constructs in the OR1200 RTL are interpreted differently by synthesis tools than by simulation tools, producing a gate-level implementation whose behavior deviates from the simulated model. Typical sources of such mismatches include non-synthesizable constructs, initial values, sensitivity list issues, X-propagation differences, and inferred latches.
Attack Vector
The attack vector is not defined in the NVD entry, and no exploit is publicly available. Exploitability depends on where the divergent logic sits within the pipeline and whether software running on the synthesized core can trigger the affected state. Integrators who ship OR1200 in security-relevant roles should treat the mismatch as a correctness defect that can invalidate software-level security guarantees.
No verified exploitation code is available for this issue. Refer to the linked research for technical analysis.
Detection Methods for CVE-2025-51679
Indicators of Compromise
- No runtime indicators of compromise are published for this hardware design defect.
- Divergence between RTL simulation output and post-synthesis gate-level simulation on the affected OR1200 commit.
- Presence of the 83ac6b OR1200 commit in project version control or vendor bill of materials.
Detection Strategies
- Run equivalence checking between the RTL and the synthesized netlist using formal tools such as Synopsys Formality or Cadence Conformal.
- Compare RTL and gate-level simulation waveforms against the same testbench and flag divergent signals.
- Audit source repositories and third-party IP manifests for the affected OR1200 commit hash.
Monitoring Recommendations
- Track updates on the openRISC mor1kx issue #161 for maintainer fixes.
- Monitor the Synfuzz CVE list for related hardware fuzzing disclosures.
- Include hardware IP components in software bill of materials (SBOM) or hardware bill of materials (HBOM) reviews.
How to Mitigate CVE-2025-51679
Immediate Actions Required
- Inventory any FPGA or ASIC projects that include the OR1200 core at commit 83ac6b.
- Halt production releases that depend on the affected commit until an updated revision is verified.
- Re-run RTL-to-gate equivalence checks on all builds using the affected core.
Patch Information
No vendor patch is listed in the NVD entry at the time of publication. Track the upstream openRISC mor1kx issue #161 for remediation guidance and rebase to a maintainer-approved revision once available.
Workarounds
- Pin projects to an earlier or maintainer-verified OR1200 revision that passes equivalence checking.
- Add synthesis directives and lint rules that reject non-synthesizable constructs implicated in the mismatch.
- Extend gate-level regression tests to cover the affected modules before tape-out or bitstream release.
No configuration example is provided because this issue requires hardware design-level remediation rather than a runtime configuration change. Refer to the upstream repository for source-level fixes.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
