{"id":"CVE-2026-107218","aliases":["GHSA-8jjq-8j9w-m2v6"],"url":"https://o3.security/vulnerability/CVE-2026-107218","summary":"Excelize: RIGHT() on supplementary-plane text slices with a negative index and panics","details":"`leftRight` (calc.go:14236) tests the length with `countUTF16String`, which counts a rune above U+FFFF as 2. The RIGHT branch on 14241 then slices `[]rune(text)` at `utf8.RuneCountInString(text)-numChars`, which counts it as 1. For text with N such runes the two measures are 2N and N, so any `numChars` between them passes the guard and gives a negative index. The `numChars < 0` check at 14216 does not help, since the value that gets through is positive.\n\nWhat makes it worth reporting is `AutoFitColWidth`, which evaluates formulas without looking like it does, so normalising an uploaded sheet is enough to reach it. One scoping correction to my own wording there: `AutoFitColWidth` was added in v2.11.0 and does not exist at v2.10.1, so on v2.10.1 the only reachable path is an explicit `CalcCellValue`.\n\nA 6,077-byte file containing two U+1D7D9 characters in A1 and  RIGHT(A1,3)  in B1 was created and then opened in a separate program without recovery enabled:\n\n```\nv2.9.1    ok\nv2.10.0   ok\nv2.10.1   panic: slice bounds out of range [-1:]\nv2.11.0   panic: slice bounds out of range [-1:]\n```\n\nSo it is a regression, not an old defect. Commit a880146 (2026-01-16) moved the guard to `countUTF16String` and left the slice on the rune index, and `git tag --contains` gives v2.10.1 and v2.11.0 only.\n\nRIGHT only. RIGHTB reaches the same function but takes the byte branch at 14225, which is internally consistent, and I probed MID and MIDB from 1 to 5 with no panic. It is the same negative-index family as GHSA-fx5j-qcqg-grpf and GHSA-48hm-4h8j-58fg, though those are shared-string lookups in the reader rather than a unit mismatch in the formula library.","published":"2026-10-07T18:29:38.606Z","modified":"2026-10-21T02:30:46.292734993Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Go","name":"github.com/xuri/excelize/v2","fixedVersion":"2.11.1-0.20260908032718-ecd99d761fe0"}],"fix":{"url":"https://github.com/qax-os/excelize/commit/ecd99d761fe0489f1ed308e2f7dc2e0502d1a396","label":"qax-os/excelize@ecd99d7"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107218.json"},{"type":"ADVISORY","url":"https://github.com/qax-os/excelize/security/advisories/GHSA-8jjq-8j9w-m2v6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107218"},{"type":"FIX","url":"https://github.com/qax-os/excelize/commit/ecd99d761fe0489f1ed308e2f7dc2e0502d1a396"},{"type":"FIX","url":"https://github.com/qax-os/excelize/pull/2390"},{"type":"PACKAGE","url":"https://github.com/qax-os/excelize"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:30:46.292734993Z"}}