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CVE-2026-107218: Excelize: RIGHT() on supplementary-plane text slices with a negative index and panics

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-10-07 · updated 2026-10-13
• Weakness: CWE-129

Description

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.10.1 to 2.11.0, RIGHT validates the requested length with UTF-16 code-unit counts but slices a rune array using Unicode code-point counts. RIGHT reaches leftRight through CalcCellValue, where countUTF16String validates one unit but utf8.RuneCountInString supplies the slice index in another. When RIGHT evaluates supplementary-plane text with a requested character count between the rune count and UTF-16 code-unit count, the inconsistent units produce a negative rune-slice index, allowing an attacker to panic during formula evaluation. No fixed version is available as of this review.

Affected products

• qax-os excelize: from 2.10.1 through 2.11.0

References

• https://github.com/qax-os/excelize/commit/ecd99d761fe0489f1ed308e2f7dc2e0502d1a396
• https://github.com/qax-os/excelize/pull/2390
• https://github.com/qax-os/excelize/security/advisories/GHSA-8jjq-8j9w-m2v6

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