Summary
Zebra's block validator undercounts transparent signature operations against the 20000-sigop block limit (MAX_BLOCK_SIGOPS), allowing it to accept blocks that zcashd rejects with bad-blk-sigops. A miner who produces such a block can split the network: Zebra nodes follow the offending chain while zcashd nodes do not.
Two distinct undercounts:
A: Coinbase Hidden Legacy Sigops
zcashd's GetLegacySigOpCount() includes the coinbase input's scriptSig. Zebra's Sigops impl skipped the coinbase input entirely, so up to ~98 sigops (the 100-byte coinbase script length cap, less the height prefix) could be hidden inside the coinbase scriptSig without being charged against the block limit.
B: Aggregate P2SH Sigops.
zcashd's GetP2SHSigOpCount() parses each P2SH input's redeem script with accurate=true and sums those sigops into the block-wide total via ConnectBlock. The check is per-block, not per-transaction, and the limit applies regardless of who mines the offending block, a miner just needs to include enough P2SH-spending transactions whose redeem scripts together exceed 20000 sigops. Zebra computed P2SH sigops only on the mempool-acceptance path (used for ZIP-317 weighting) and never accumulated them during block validation. A block whose aggregate redeem-script sigops exceed 20000 (e.g. 1334 P2SH spends × 15 sigops = 20010) would be accepted by Zebra and rejected by zcashd.
Workarounds
None. Operators relying on Zebra for consensus should upgrade.
Resources
MAX_BLOCK_SIGOPSconstant inherited from Bitcoin via the Zcash protocol spec's §7.6 catch-all "Other rules inherited from Bitcoin", tracked for explicit documentation in zcash/zips#568.zcashdGetLegacySigOpCount: https://github.com/zcash/zcash/blob/v6.11.0/src/main.cpp#L826-L836zcashdGetP2SHSigOpCount: https://github.com/zcash/zcash/blob/v6.11.0/src/main.cpp#L840-L852zcashdConnectBlockaggregates per-tx sigops and compares againstMAX_BLOCK_SIGOPS.
Impact
CVE-2026-44498 has a CVSS score of 7.5 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.4.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Fixed in this release: https://github.com/ZcashFoundation/zebra/releases/tag/v4.4.0.
Frequently Asked Questions
- What is CVE-2026-44498? CVE-2026-44498 is a critical-severity security vulnerability in zebrad (rust), affecting versions < 4.4.0. It is fixed in 4.4.0.
- How severe is CVE-2026-44498? CVE-2026-44498 has a CVSS score of 7.5 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of zebrad are affected by CVE-2026-44498? zebrad (rust) versions < 4.4.0 is affected.
- Is there a fix for CVE-2026-44498? Yes. CVE-2026-44498 is fixed in 4.4.0. Upgrade to this version or later.
- Is CVE-2026-44498 exploitable, and should I be worried? Whether CVE-2026-44498 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44498 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44498? Upgrade
zebradto 4.4.0 or later.