Backporting Upstream Bitcoin Core CVEs to a Post-Quantum Architecture
Software architectures that fork mature codebases face a continuous operational challenge: maintaining alignment with upstream security advisories. When building btq-core as a post-quantum Layer 1 network, we adopted Bitcoin Core 26.0 as our foundational baseline. The goal was deliberate: retain Bitcoin’s proven UTXO model, memory management discipline, and transaction verification flow while adding a post-quantum signature standard, ML-DSA-44, alongside the elliptic curve schemes.
On August 1, 2026, an internal review logged as issue #120 triaged thirteen published Bitcoin Core advisories and found that six applied to the btq-core 26.0 baseline. By August 6, 2026, five days later, all six fixes were merged. One of them, for a CPU denial of service issue, reduced sighash work on a dense test transaction from 147 ms to 2.4 ms.
Dissecting the 61x sighash benchmark
The most striking result from this cycle comes from the fix for CVE-2025–46598, which upstream rates Medium. Specially crafted unconfirmed transactions could take seconds each to validate and could be repeated at no cost to the sender.
Legacy sighash re-serializes the whole transaction on every call, so a script that forces many sighashes costs quadratic work. The backport in PR #149 caches the SHA-256 midstate so that a repeated script code within one input serializes the transaction once.
The measurement in PR #149 used a synthetic 200-input transaction taking 20,000 sighashes over one script code. That workload went from 147 milliseconds to 2.4 milliseconds, a 61x speedup. This figure measures sighash work on that transaction and does not describe all validation.
Upstream’s two other mitigations are also in: witness-stripping detection without re-running scripts (PR #139), and one script run per failing input (PR #149). BTQ also adds the signature version to the cache key, because CheckDilithiumSignature chooses its path by signature version inside a single input.
Script interpreter memory safety: CVE-2024–52911
The August set also included CVE-2024–52911, the only High of the six. A specially crafted block could remotely crash a node through a use-after-free in script validation.
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ConnectBlock dispatches script checks to background threads, and each check holds a pointer into precomputed transaction data. Our tree declared the two objects in the wrong order, so that data was freed before the check queue finished. The fix in PR #135 corrects the order.
The four additional upstream security fixes
In addition to the script validation and sighash fixes, the set closed four other advisories:
- CVE-2025–54604: repeated spoofed self-connections could fill the disk through unconditional logging.
- CVE-2025–54605: repeated invalid blocks could fill the disk the same way. One backported change, rate limits on log sources, closes both.
- CVE-2025–46597: a crash on 32-bit systems in an edge case, closed by capping
-maxmempool. - CVE-2024–52919: a crash from prolonged address message spam, closed by widening the addrman entry ID past 32 bits.
What the triage showed
Issue #120 also recorded that the tree had no upstream merges after its December 2023 baseline. Seven of the thirteen advisories did not apply, and some patches could not be cherry-picked. PR #137, for example, was applied by hand because later upstream code and BTQ’s renames blocked a clean apply.
Our post-quantum work adds NIST-standardized ML-DSA-44 signatures on top of that 26.0 baseline. Tracking upstream advisories remains regular work for the project.
Current deployment status on testnet
All six fixes are in the v0.5.0-testnet release of August 20, 2026.
Node operators on older builds should update. The issue and pull requests above are public in the btq-core repository.
