CVE-2025-66559: taikoxyz taiko-mono · Improper Validation of Array Index
Affects taikoxyz taiko-monoSource CVE Database V5
Not known to be exploited · CVSS 8.0 High.
Data as of 26 Oct 2026, 10:12 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:UExploitation evidence
Disclosed: evidence found.
CVE published 4 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
GitHubtaikoxyz/taiko-monopkg:github/taikoxyz/taiko-monoOther threats | Affected
| Fixed in– |
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AI-suggested
- Upgrade taiko-mono to a version later than 2.3.1 once the vendor releases a patch addressing CVE-2025-66559.
- Until a patch is available, implement additional validation checks in the batch verification process to ensure that transition IDs do not reference out-of-bound or next-batch indices.
- Conduct thorough code audits focusing on array index handling and boundary conditions in smart contract functions related to batch and transition verification.
- Deploy monitoring tools to detect anomalies in batch verification results or unexpected changes in verifiedTransitionId pointers.
- Engage with the taikoxyz community and maintain awareness of updates or mitigations shared by the vendor or security researchers.
- For organizations building on top of taiko-mono, implement fallback or verification mechanisms to cross-check rollup state integrity externally.
- Incorporate security testing, including fuzzing and static analysis, targeting array index usage in smart contracts to preempt similar vulnerabilities.
Description
Taiko Alethia is an Ethereum-equivalent, permissionless, based rollup designed to scale Ethereum without compromising its fundamental properties. In 2.3.1 and earlier, TaikoInbox._verifyBatches (packages/protocol/contracts/layer1/based/TaikoInbox.sol:627-678) advanced the local tid to whatever transition matched the current blockHash before knowing whether that batch would actually be verified. When the loop later broke (e.g., cooldown window not yet passed or transition invalidated), the function still wrote that newer tid into batches[lastVerifiedBatchId].verifiedTransitionId after decrementing batchId. Result: the last verified batch could end up pointing at a transition index from the next batch (often zeroed), corrupting the verified chain pointer.