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CVE-2026-107218 medium CVSS 5.3

Vulnerability in github.com/xuri/excelize/v2 (CVE-2026-107218)

Summary

Vulnerability in github.com/xuri/excelize/v2 (CVE-2026-107218). Risk of unauthorized operations or information disclosure. Exploitable via leftRight. Mitigation: upgrade to 2.11.1-0.20260908032718-ecd99d761fe0 or later.

Original description

The description as published by the source.

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-ind…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-107218 has been found in github.com/xuri/excelize/v2.
Attackers can target a specific entry point like leftRight over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade github.com/xuri/excelize/v2 to 2.11.1-0.20260908032718-ecd99d761fe0 or later.
If unsure, ask your IT team or search "github.com/xuri/excelize/v2 CVE-2026-107218" on the vendor's site.

CVE-2026-107218 (github.com/xuri/excelize/v2) — CWE-129 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: leftRight / countUTF16String / numChars / AutoFitColWidth
Patched: 2.11.1-0.20260908032718-ecd99d761fe0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-129) exists in github.com/xuri/excelize/v2. Attackers reach the vulnerable code path via leftRight without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/xuri/excelize/v2. Attack surface: leftRight / countUTF16String / numChars / AutoFitColWidth.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 2.11.1-0.20260908032718-ecd99d761fe0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/xuri/excelize/v2' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'github.com/xuri/excelize/v2' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で github.com/xuri/excelize/v2 を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade github.com/xuri/excelize/v2 to 2.11.1-0.20260908032718-ecd99d761fe0

    ステージング環境で 2.11.1-0.20260908032718-ecd99d761fe0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

go github.com/xuri/excelize/v2
[{"type":"SEMVER","events":[{"introduced":"2.10.1"},{"fixed":"2.11.1-0.20260908032718-ecd99d761fe0"}]}]

References

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