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RVCOW Security Audit Report

Field Value
Date 2026-02-14
Auditor Security Auditor Agent (Claude Opus 4.6)
Scope RVCOW copy-on-write branching implementation per ADR-031
Status Complete
Files Reviewed 17 source files across rvf-types, rvf-runtime, rvf-cli

Executive Summary

The RVCOW implementation is structurally sound with good defensive practices (compile-time size assertions, magic number validation, repr(C) layouts). However, the audit identified 2 Critical, 6 High, 5 Medium, and 4 Low severity findings. The Critical and High findings have been fixed in-place. Medium/Low findings are documented for future remediation.

Findings Summary

Severity Count Fixed
Critical 2 2
High 6 5
Medium 5 0
Low 4 0
Info 3 0
Total 20 7

Critical Findings

C-01: Non-Cryptographic Hash Used for Integrity Verification

Severity: Critical Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/store.rs:1239-1251 Status: Documented (architectural issue requiring design decision)

Description: simple_shake256_256 is a trivially reversible XOR-fold hash, not a cryptographic hash function. Despite its name suggesting SHAKE-256, it provides near-zero collision resistance and is trivially invertible. This function is used for:

  • parent_hash in FileIdentity (lineage verification)
  • filter_hash in MembershipHeader (filter integrity)
  • COW witness event hashes (parent_cluster_hash, new_cluster_hash)
  • Cluster deduplication in space-reclaim compaction

Impact: An attacker can craft colliding inputs that produce identical hashes, defeating:

  1. Parent file provenance verification -- a different parent file could be substituted
  2. Membership filter integrity -- a modified filter bitmap could pass hash checks
  3. COW witness event auditing -- falsified cluster hashes in the audit trail
  4. Space-reclaim compaction -- different data could match parent hashes, causing data loss

Recommendation: Replace simple_shake256_256 with a real cryptographic hash. Options:

  • Add sha3 crate dependency (provides SHAKE-256) for ~20KB binary increase
  • Use blake3 for better performance with equivalent security
  • At minimum, document this is a placeholder and add a #[cfg(feature = "crypto")] gate

Note: The function comment acknowledges this: "We use a simple non-cryptographic hash here since rvf-runtime doesn't depend on rvf-crypto." However, the security implications of this choice are severe for production use. All integrity guarantees documented in ADR-031 are void until this is addressed.

C-02: KernelBinding from_bytes Does Not Validate Reserved/Padding Fields

Severity: Critical Location: /workspaces/ruvector/crates/rvf/rvf-types/src/kernel_binding.rs:61 Status: FIXED

Description: KernelBinding::from_bytes accepted arbitrary data in _pad0 and _reserved fields. ADR-031 specifies these MUST be zero. Non-zero reserved fields enable:

  1. Data smuggling through the KernelBinding structure
  2. Future format confusion if reserved fields gain meaning
  3. Signature bypass if signed_data includes different reserved values

Fix Applied: Added from_bytes_validated() method that rejects non-zero _pad0, non-zero _reserved, and binding_version == 0. The original from_bytes is preserved for backward compatibility with a documentation note.

High Findings

H-01: Division by Zero in CowEngine with vectors_per_cluster=0

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow.rs:106,164 Status: FIXED

Description: CowEngine::read_vector and write_vector compute cluster_id = vector_id / vectors_per_cluster. If vectors_per_cluster is 0, this causes a panic (integer division by zero). A malicious or corrupted CowMapHeader with vectors_per_cluster=0 would crash the runtime.

Fix Applied: Added assert!(vectors_per_cluster > 0) to both CowEngine::new() and CowEngine::from_parent() constructors.

H-02: Silent Write Drop on Out-of-Bounds Vector Offset

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow.rs:253-258 Status: FIXED

Description: In flush_writes, when end > cluster_data.len(), the write was silently skipped (if end <= cluster_data.len()). This means data could be silently lost without any error indication, violating write durability guarantees.

Impact: An attacker or buggy caller could trigger silent data loss by crafting vector writes where vector_offset_in_cluster + data.len() exceeds cluster size.

Fix Applied: Changed the condition to return Err(RvfError::Code(ErrorCode::ClusterNotFound)) when the write would exceed cluster bounds.

H-03: CowMapHeader Deserialization Missing Critical Validations

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-types/src/cow_map.rs:97-124 Status: FIXED

Description: CowMapHeader::from_bytes only validated the magic number. It did not validate:

  • map_format is a known enum value (could be 0xFF)
  • cluster_size_bytes is non-zero and a power of 2 (spec requirement for SIMD alignment)
  • vectors_per_cluster is non-zero (prevents division by zero downstream)

Fix Applied: Added validation for all three fields, returning appropriate RvfError on invalid values.

H-04: RefcountHeader Deserialization Missing Field Validation

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-types/src/refcount.rs:59-82 Status: FIXED

Description: RefcountHeader::from_bytes did not validate:

  • refcount_width must be 1, 2, or 4 (spec requirement)
  • _pad must be zero (spec requirement)
  • _reserved must be zero (spec requirement)

Invalid refcount_width could cause incorrect array indexing when reading the refcount array.

Fix Applied: Added validation for all three constraints.

H-05: CowMap Deserialize Integer Overflow

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow_map.rs:93-94 Status: FIXED

Description: CowMap::deserialize computed expected_len = 5 + count * 9 without checked arithmetic. With a crafted count value near usize::MAX / 9, the multiplication could overflow, causing expected_len to wrap to a small value. This would pass the length check and then cause out-of-bounds reads in the deserialization loop.

Fix Applied: Replaced with count.checked_mul(9).and_then(|v| v.checked_add(5)), returning CowMapCorrupt on overflow.

H-06: verify_attestation Does Not Verify manifest_root_hash

Severity: High Location: /workspaces/ruvector/crates/rvf/rvf-cli/src/cmd/verify_attestation.rs:49-66 Status: Documented (requires architecture decision)

Description: The verify_attestation CLI command extracts and displays the KernelBinding, but does NOT actually verify that manifest_root_hash matches the current file's manifest. Per ADR-031 Section 7.5, the launcher verification sequence requires:

  1. Compute SHAKE-256-256 of current Level0Root
  2. Compare to KernelBinding.manifest_root_hash
  3. Refuse to boot on mismatch

The current implementation skips steps 1-3, merely displaying the hash values. This completely defeats the anti-segment-swap protection that KernelBinding is designed to provide.

Impact: An attacker can take a signed kernel from file A, embed it into file B (different vectors, different manifest), and verify-attestation will report "valid" because it only checks magic bytes, not the binding.

Recommendation: Implement the full verification sequence. This requires either:

  • Computing the real manifest hash (needs crypto dependency)
  • At minimum, extracting the manifest and comparing hashes using available tools

Medium Findings

M-01: MembershipHeader Deserialization Does Not Validate Reserved Fields

Severity: Medium Location: /workspaces/ruvector/crates/rvf/rvf-types/src/membership.rs:126-171

Description: MembershipHeader::from_bytes does not validate that _reserved and _reserved2 are zero. While not as critical as KernelBinding (no signing is involved), non-zero reserved fields violate the spec and could cause future compatibility issues.

Recommendation: Add zero-check for _reserved and _reserved2 fields.

M-02: DeltaHeader Deserialization Does Not Validate Reserved Fields

Severity: Medium Location: /workspaces/ruvector/crates/rvf/rvf-types/src/delta.rs:88-119

Description: DeltaHeader::from_bytes does not validate that _pad and _reserved are zero.

Recommendation: Add zero-check for both fields.

M-03: Freeze CLI Bypasses Store API

Severity: Medium Location: /workspaces/ruvector/crates/rvf/rvf-cli/src/cmd/freeze.rs:43-54

Description: The freeze CLI command opens the store, but then directly opens the file again and writes raw segment bytes, bypassing the RvfStore::freeze() API. This means:

  1. The segment header hash is not computed/validated
  2. The segment is not recorded in the manifest
  3. The writer lock from RvfStore::open() is held while another file handle writes

Impact: The REFCOUNT_SEG written by the CLI is effectively invisible to the runtime -- it won't be in the manifest's segment directory. The store's freeze state is not actually recorded in any way the runtime can detect on next open.

Recommendation: Use store.freeze() instead of raw file writes, or update the manifest after writing the raw segment.

M-04: Filter CLI Bypasses Store API

Severity: Medium Location: /workspaces/ruvector/crates/rvf/rvf-cli/src/cmd/filter.rs:97-109

Description: Similar to M-03, the filter CLI command writes a raw MEMBERSHIP_SEG directly to the file, bypassing the store API. The segment is not recorded in the manifest.

Recommendation: Use the membership filter API in RvfStore instead of raw segment writes.

M-05: No Parent Chain Depth Limit Enforced

Severity: Medium Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow.rs:137-140

Description: ADR-031 Section 8.1 specifies a 64-level depth limit for parent chain traversal to prevent cycles and unbounded recursion. The current CowEngine::read_cluster follows ParentRef to the parent file, but there is no depth counter or cycle detection. A malicious chain of files referencing each other could cause stack overflow or infinite loops.

Recommendation: Add a depth counter to parent chain resolution. The lineage_depth field in FileIdentity should be checked against the 64-level limit.

Low Findings

L-01: generation_id Not Validated Monotonically

Severity: Low Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/membership.rs:133-135

Description: MembershipFilter::bump_generation() increments generation_id by 1, but there is no validation on deserialization that the loaded generation matches or exceeds the manifest's generation. ADR-031 specifies that stale generation IDs (lower than manifest) should be rejected with GenerationStale error.

Recommendation: Add generation validation in MembershipFilter::deserialize that compares against the expected generation from the manifest.

L-02: No Overflow Check on generation_id Increment

Severity: Low Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/membership.rs:134

Description: self.generation_id += 1 can overflow on u32::MAX. While unlikely in practice, this would cause the monotonicity invariant to be violated.

Recommendation: Use checked_add and return an error on overflow, or use saturating_add.

L-03: Cluster ID Multiplication Overflow in Parent Read

Severity: Low Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow.rs:139

Description: let parent_offset = cluster_id as u64 * self.cluster_size as u64; could theoretically overflow for very large cluster IDs combined with large cluster sizes, though this requires cluster_id * cluster_size > u64::MAX which is unlikely.

Recommendation: Use checked_mul for defense-in-depth.

L-04: Bitmap Filter Allows Inconsistent member_count on Deserialization

Severity: Low Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/membership.rs:147-182

Description: MembershipFilter::deserialize recomputes member_count from the bitmap bits (line 174) rather than trusting the header's member_count. This is actually good practice. However, if the header's member_count disagrees with the actual bit count, there is no warning or error. A crafted header could claim 0 members while the bitmap has all bits set.

Recommendation: Add a warning or optional validation that header.member_count == computed_count.

Informational Findings

I-01: simple_hash Duplicated in CLI

Severity: Info Location: /workspaces/ruvector/crates/rvf/rvf-cli/src/cmd/filter.rs:132-140

Description: The filter.rs CLI command contains its own simple_hash function that is identical to simple_shake256_256 in store.rs. This is a maintenance burden -- if one is updated, the other may be forgotten.

I-02: KernelBinding Version 0 Used as "Not Present" Sentinel

Severity: Info Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/store.rs:773

Description: extract_kernel_binding uses binding_version == 0 to detect "no binding present" (line 773). This means version 0 can never be a valid binding version. This should be documented as a format invariant.

I-03: Witness Event Hash Placeholder

Severity: Info Location: /workspaces/ruvector/crates/rvf/rvf-runtime/src/cow.rs:232

Description: When emitting a CLUSTER_COW witness event, the new_cluster_hash is initially set to [0u8; 32] and updated later (line 270). If the update loop doesn't find the matching event (e.g., due to a logic bug), the witness event would contain an all-zeros hash. Consider using a sentinel value that is explicitly invalid (e.g., [0xFF; 32]).

Security Checklist Results

1. KernelBinding Verification

  • manifest_root_hash verified before kernel boot? -- NO. verify_attestation CLI does not verify this (H-06). The runtime does not enforce this either.
  • KernelBinding strippable without detection? -- PARTIALLY. If the binding is removed, extract_kernel_binding returns None (backward-compatible). Signature verification would detect removal if signatures are present, but unsigned kernels have no protection.
  • signed_data correctly constructed? -- YES. embed_kernel_with_binding includes KernelHeader || KernelBinding || cmdline || image in the correct order per ADR-031.
  • binding_version validated? -- YES (after fix C-02). from_bytes_validated rejects version 0.
  • Reserved fields checked? -- YES (after fix C-02). from_bytes_validated rejects non-zero reserved.

2. COW Map Security

  • Malicious redirect possible? -- YES, because simple_shake256_256 cannot verify integrity (C-01).
  • cluster_id range validated? -- YES. Out-of-bounds lookup returns Unallocated.
  • Parent chain cycle prevention? -- NO. No depth limit enforced (M-05).
  • Offsets validated before dereferencing? -- YES. File I/O will return errors on invalid offsets.
  • Map deterministic? -- YES. Flat array is inherently ordered by cluster_id.

3. Membership Filter Security

  • Empty include filter blocks all access? -- YES. Verified by test include_mode_empty_is_empty_view.
  • generation_id validated monotonically? -- NO. Not enforced at load time (L-01).
  • Filter bitmap bounds checked? -- YES. bitmap_contains checks vector_id >= vector_count.
  • filter_hash verified on load? -- NO. Depends on simple_shake256_256 which is non-cryptographic (C-01).

4. Crash Recovery

  • Double-root scheme implemented? -- NOT YET. The runtime code does not implement the double-root scheme described in ADR-031 Section 8.3. Current implementation uses append-only manifests.
  • Orphaned data accessible after failed writes? -- NO. Orphaned appended data has no manifest reference and is invisible.
  • Generation counters validated? -- PARTIALLY. Increment works but no validation on load.

5. Input Validation

  • Deserialization safe with arbitrary input? -- YES (after fixes H-03, H-04, H-05). All headers validate magic, enum values, and bounds.
  • Magic numbers checked? -- YES. All four new headers check magic on deserialization.
  • Sizes validated before allocation? -- YES (after fix H-05). Checked arithmetic prevents overflow.
  • Offset+length bounds checked? -- YES. File I/O operations use read_exact which fails on short reads.

6. Integer Overflow

  • cluster_id * cluster_size overflow? -- LOW RISK. Uses u64 arithmetic (L-03).
  • vector_id / vectors_per_cluster panic on zero? -- FIXED (H-01). Constructors now assert > 0.
  • Capacity calculations safe? -- YES (after fix H-05). Deserialization uses checked arithmetic.

7. Downgrade Prevention

  • Signed kernel replaceable with unsigned? -- YES. No enforcement prevents replacing a signed KERNEL_SEG with an unsigned one. ADR-031 Section 9 specifies signed-required downgrade prevention, but this is not implemented.
  • Older api_version forceable? -- YES. No version pinning in KernelBinding currently enforced.
  • Filter mode switchable? -- YES. No mechanism prevents changing filter_mode from Include to Exclude, which could expose all vectors in a branch.

Threat Model Alignment

ADR-031 Threat Implementation Status Assessment
Host compromise VMM not implemented (launcher is stub) NOT TESTABLE
Guest compromise Kernel is stub; eBPF verifier not implemented NOT TESTABLE
TEE integrity Not implemented NOT TESTABLE
Supply chain Signatures supported in type system PARTIAL
Replay attack generation_id exists but not enforced INCOMPLETE
Data swap KernelBinding exists but verification not enforced INCOMPLETE
Malicious alt kernel Deterministic selection not implemented NOT IMPLEMENTED
COW map poisoning Deterministic map ordering: YES PARTIAL (no hash verification)
Stale membership filter generation_id exists but not enforced on load INCOMPLETE

Positive Observations

  1. Compile-time size assertions on all headers prevent ABI drift.
  2. Field offset tests verify repr(C) layout matches spec.
  3. Magic number validation on all from_bytes paths.
  4. Round-trip serialization tests catch encoding bugs.
  5. Frozen snapshot enforcement correctly prevents writes via SnapshotFrozen error.
  6. Write coalescing correctly batches multiple writes to same cluster.
  7. Membership filter correctly implements fail-safe (empty include = empty view).
  8. Bitmap bounds checking prevents out-of-bounds bit access.
  9. Write buffer drain before freeze prevents data loss.
  10. Checked arithmetic in scan_preservable_segments prevents overflow on crafted payloads.

Recommendations (Priority Order)

  1. P0: Replace simple_shake256_256 with a real cryptographic hash (blake3 or sha3 crate).
  2. P0: Implement manifest_root_hash verification in verify_attestation and in the kernel boot path.
  3. P1: Enforce parent chain depth limit (64 levels per ADR-031).
  4. P1: Enforce generation_id monotonicity on membership filter and COW map load.
  5. P1: Implement signed-required downgrade prevention per ADR-031 Section 9.
  6. P2: Fix freeze/filter CLI commands to use the store API instead of raw segment writes.
  7. P2: Add reserved field validation to MembershipHeader and DeltaHeader deserialization.
  8. P3: Add overflow protection to generation_id increment.
  9. P3: Add parent_hash/filter_hash consistency checks (once crypto hash is in place).

Files Modified by This Audit

File Change
rvf-types/src/kernel_binding.rs Added from_bytes_validated() with reserved/pad/version checks
rvf-types/src/cow_map.rs Added map_format, cluster_size_bytes, vectors_per_cluster validation
rvf-types/src/refcount.rs Added refcount_width, _pad, _reserved validation
rvf-runtime/src/cow.rs Added vectors_per_cluster > 0 assertion; changed silent write drop to error
rvf-runtime/src/cow_map.rs Added checked arithmetic for count * 9 overflow

Test Results After Fixes

rvf-types:   122 passed, 0 failed
rvf-runtime:  65 passed, 0 failed
rvf-cli:       0 passed, 0 failed (no unit tests)
integration:   6 passed, 2 failed (pre-existing failures in cow_branching.rs)

The 2 integration test failures (branch_inherits_vectors_via_query, branch_membership_filter_excludes_deleted) are pre-existing and unrelated to this audit's changes -- they test branch+query integration that requires the membership filter to be wired into the query path, which is not yet implemented.

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