Excelize: RIGHT() on supplementary-plane text slices with a negative index and panics

{
  "id": "576d757dbd3a3c44a7b89be9ff7fe9546bfd340ec24fa07c02bb5af95fa9dff3",
  "url": "https://osv.dev/vulnerability/GHSA-8jjq-8j9w-m2v6",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Excelize: RIGHT() on supplementary-plane text slices with a negative index and panics",
    "summary": "`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. What 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`. A 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: ``` v2.9.1 ok v2.10.0 ok v2.10.1 panic: slice bounds out of range [-1:] v2.11.0 panic: slice bounds out of range [-1:] ``` So 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. RIGHT 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 GHS",
    "evidence": "osv:GHSA-8jjq-8j9w-m2v6",
    "products": [
      {
        "name": {
          "value": "github.com/xuri/excelize/v2",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "2.11.1-0.20260908032718-ecd99d761fe0",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "GHSA-8jjq-8j9w-m2v6",
      "aliases": [
        "CVE-2026-107218",
        "GHSA-8jjq-8j9w-m2v6"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "2.10.1"
                },
                {
                  "fixed": "2.11.1-0.20260908032718-ecd99d761fe0"
                }
              ]
            }
          ],
          "package": {
            "name": "github.com/xuri/excelize/v2",
            "purl": "pkg:golang/github.com/xuri/excelize/v2",
            "ecosystem": "Go"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-8jjq-8j9w-m2v6/GHSA-8jjq-8j9w-m2v6.json"
          }
        }
      ],
      "modified": "2026-10-07T20:30:05.877569663Z",
      "provider": "osv",
      "references": [
        "https://github.com/qax-os/excelize/security/advisories/GHSA-8jjq-8j9w-m2v6",
        "https://github.com/qax-os/excelize/pull/2390",
        "https://github.com/qax-os/excelize/commit/ecd99d761fe0489f1ed308e2f7dc2e0502d1a396",
        "https://github.com/qax-os/excelize"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-129"
        ],
        "severity": "MODERATE",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-07T20:23:26Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-107218",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 97233,
  "published_at": "2026-10-07T20:23:26+00:00"
}