{"id":"CVE-2020-26265","aliases":["EUVD-2021-1427","GHSA-xw37-57qp-9mm4","GO-2021-0105"],"status":"published","title":"Consensus flaw during block processing","description":"Go Ethereum, or \"Geth\", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.0092,"percentile":0.60581,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-682"],"published":"2020-12-11T16:45:15Z","modified":"2026-10-20T10:52:56Z","fixes":[{"ecosystem":"Go","package":"github.com/ethereum/go-ethereum","fixed_in":["1.9.20"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"Go","package":"github.com/ethereum/go-ethereum","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.9.4"},{"fixed":"1.9.20"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/ethereum/go-ethereum","ranges":[{"type":"SEMVER","events":[{"introduced":"1.9.4"},{"fixed":"1.9.20"}]}]},{"source":"osv","ecosystem":"Go","package":"github.com/ethereum/go-ethereum","ranges":[{"type":"SEMVER","events":[{"introduced":"1.9.4"},{"fixed":"1.9.20"}]}]}],"products":[{"vendor":"ethereum","product":"go-ethereum"},{"vendor":"ethereum","product":"go_ethereum"}],"references":[{"url":"https://github.com/ethereum/go-ethereum/security/advisories/GHSA-xw37-57qp-9mm4","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://github.com/ethereum/go-ethereum/releases/tag/v1.9.20","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2020-26265","tags":["advisory"]},{"url":"https://github.com/ethereum/go-ethereum/pull/21409","tags":["web"]},{"url":"https://github.com/ethereum/go-ethereum/pull/21080","tags":["web","fix"]},{"url":"https://github.com/ethereum/go-ethereum/commit/87c0ba92136a75db0ab2aba1046d4a9860375d6a","tags":["web","fix"]},{"url":"https://pkg.go.dev/vuln/GO-2021-0105","tags":["web"]},{"url":"https://github.com/advisories/GHSA-xw37-57qp-9mm4"},{"url":"https://github.com/ethereum/go-ethereum","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2020-26265","title":"Consensus flaw during block processing","description":"Go Ethereum, or \"Geth\", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.","status":"published","published":"2020-12-11T16:45:15Z","modified":"2024-08-04T15:56:03.493Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-682"],"updated_at":"2026-11-02T14:35:46.129376Z"}],"euvd":[{"id":"EUVD-2021-1427","description":"Go Ethereum, or \"Geth\", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.","status":"published","published":"2020-12-11T16:45:15Z","modified":"2024-08-04T15:56:03Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-03T03:07:15.778249Z"}],"ghsa":[{"id":"GHSA-xw37-57qp-9mm4","title":"Consensus flaw during block processing in github.com/ethereum/go-ethereum","description":"### Impact\n\nA consensus-vulnerability in Geth could cause a chain split, where vulnerable versions refuse to accept the canonical chain. \n\n### Description\n\n\nA flaw was repoted at 2020-08-11 by John Youngseok Yang (Software Platform Lab), where a particular sequence of transactions could cause a consensus failure.\n\n- Tx 1:\n  - `sender` invokes `caller`.\n  - `caller` invokes `0xaa`. `0xaa` has 3 wei, does a self-destruct-to-self\n  - `caller` does a  `1 wei` -call to `0xaa`, who thereby has 1 wei (the code in `0xaa` still executed, since the tx is still ongoing, but doesn't redo the selfdestruct, it takes a different path if callvalue is non-zero)\n\n- Tx 2:\n  - `sender` does a 5-wei call to 0xaa. No exec (since no code). \n\nIn geth, the result would be that `0xaa` had `6 wei`, whereas OE reported (correctly) `5` wei. Furthermore, in geth, if the second tx was not executed, the `0xaa` would be destructed, resulting in `0 wei`. Thus obviously wrong. \n\nIt was determined that the root cause was this [commit](https://github.com/ethereum/go-ethereum/commit/223b950944f494a5b4e0957fd9f92c48b09037ad) from [this PR](https://github.com/ethereum/go-ethereum/pull/19953). The semantics of `createObject` was subtly changd, into returning a non-nil object (with `deleted=true`) where it previously did not if the account had been destructed. This return value caused the new object to inherit the old `balance`:\n\n```golang\nfunc (s *StateDB) CreateAccount(addr common.Address) {\n\tnewObj, prev := s.createObject(addr)\n\tif prev != nil {\n\t\tnewObj.setBalance(prev.data.Balance)\n\t}\n}\n```\n\nIt was determined that the minimal possible correct fix was\n\n```diff\n+++ b/core/state/statedb.go\n@@ -589,7 +589,10 @@ func (s *StateDB) createObject(addr common.Address) (newobj, prev *stateObject)\n                s.journal.append(resetObjectChange{prev: prev, prevdestruct: prevdestruct})\n        }\n        s.setStateObject(newobj)\n-       return newobj, prev\n+       if prev != nil \u0026\u0026 !prev.deleted {\n+               return newobj, prev\n+       }\n+       return newobj, nil\n```\n\n### Patches\n\nSee above. The fix was included in Geth `v1.9.20` \"Paragade\".\n\n### Credits\n\nThe bug was found by @johnyangk and reported via bounty@ethereum.org.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [go-ethereum](https://github.com/ethereum/go-ethereum)\n* Email us at [security@ethereum.org](mailto:security@ethereum.org)","status":"published","published":"2021-06-29T21:14:16Z","modified":"2023-02-14T20:54:32Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-682"],"updated_at":"2026-11-02T14:36:45.67005Z"}],"nvd":[{"id":"CVE-2020-26265","description":"Go Ethereum, or \"Geth\", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.","status":"published","published":"2020-12-11T17:15:12.87Z","modified":"2026-06-17T03:07:57.407Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium","assessor":"primary"},{"version":"2.0","score":3.5,"vector":"AV:N/AC:M/Au:S/C:N/I:P/A:N","level":"low","assessor":"primary"}],"cwes":["CWE-682"],"updated_at":"2026-11-02T14:06:27.10541Z"}],"osv":[{"id":"CVE-2020-26265","description":"Go Ethereum, or \"Geth\", is the official Golang implementation of the Ethereum protocol. In Geth from version 1.9.4 and before version 1.9.20 a consensus-vulnerability could cause a chain split, where vulnerable versions refuse to accept the canonical chain. The fix was included in the Paragade release version 1.9.20. No individual workaround patches have been made -- all users are recommended to upgrade to a newer version.","status":"published","published":"2020-12-11T17:15:12.87Z","modified":"2026-10-20T10:52:56.497533007Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"updated_at":"2026-11-02T15:44:16.248747Z"},{"id":"GHSA-xw37-57qp-9mm4","title":"Consensus flaw during block processing in github.com/ethereum/go-ethereum","description":"### Impact\n\nA consensus-vulnerability in Geth could cause a chain split, where vulnerable versions refuse to accept the canonical chain. \n\n### Description\n\n\nA flaw was repoted at 2020-08-11 by John Youngseok Yang (Software Platform Lab), where a particular sequence of transactions could cause a consensus failure.\n\n- Tx 1:\n  - `sender` invokes `caller`.\n  - `caller` invokes `0xaa`. `0xaa` has 3 wei, does a self-destruct-to-self\n  - `caller` does a  `1 wei` -call to `0xaa`, who thereby has 1 wei (the code in `0xaa` still executed, since the tx is still ongoing, but doesn't redo the selfdestruct, it takes a different path if callvalue is non-zero)\n\n- Tx 2:\n  - `sender` does a 5-wei call to 0xaa. No exec (since no code). \n\nIn geth, the result would be that `0xaa` had `6 wei`, whereas OE reported (correctly) `5` wei. Furthermore, in geth, if the second tx was not executed, the `0xaa` would be destructed, resulting in `0 wei`. Thus obviously wrong. \n\nIt was determined that the root cause was this [commit](https://github.com/ethereum/go-ethereum/commit/223b950944f494a5b4e0957fd9f92c48b09037ad) from [this PR](https://github.com/ethereum/go-ethereum/pull/19953). The semantics of `createObject` was subtly changd, into returning a non-nil object (with `deleted=true`) where it previously did not if the account had been destructed. This return value caused the new object to inherit the old `balance`:\n\n```golang\nfunc (s *StateDB) CreateAccount(addr common.Address) {\n\tnewObj, prev := s.createObject(addr)\n\tif prev != nil {\n\t\tnewObj.setBalance(prev.data.Balance)\n\t}\n}\n```\n\nIt was determined that the minimal possible correct fix was\n\n```diff\n+++ b/core/state/statedb.go\n@@ -589,7 +589,10 @@ func (s *StateDB) createObject(addr common.Address) (newobj, prev *stateObject)\n                s.journal.append(resetObjectChange{prev: prev, prevdestruct: prevdestruct})\n        }\n        s.setStateObject(newobj)\n-       return newobj, prev\n+       if prev != nil \u0026\u0026 !prev.deleted {\n+               return newobj, prev\n+       }\n+       return newobj, nil\n```\n\n### Patches\n\nSee above. The fix was included in Geth `v1.9.20` \"Paragade\".\n\n### Credits\n\nThe bug was found by @johnyangk and reported via bounty@ethereum.org.\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Open an issue in [go-ethereum](https://github.com/ethereum/go-ethereum)\n* Email us at [security@ethereum.org](mailto:security@ethereum.org)","status":"published","published":"2021-06-29T21:14:16Z","modified":"2026-09-10T03:49:15.235306786Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N","level":"medium"}],"cwes":["CWE-682"],"updated_at":"2026-11-02T15:47:00.604718Z"},{"id":"GO-2021-0105","title":"Consensus flaw in github.com/ethereum/go-ethereum","description":"Due to an incorrect state calculation, a specific set of transactions could cause a consensus disagreement, causing users of this package to reject a canonical chain.","status":"published","published":"2021-07-28T18:08:05Z","modified":"2024-05-20T16:03:47Z","updated_at":"2026-11-02T15:47:00.604718Z"}]}}