Summary
Excelize: RIGHT() on supplementary-plane text slices with a negative index and panics
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 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.
Impact
CVE-2026-107218 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.11.1-0.20260908032718-ecd99d761fe0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-107218? CVE-2026-107218 is a medium-severity security vulnerability in github.com/xuri/excelize/v2 (go), affecting versions >= 2.10.1, < 2.11.1-0.20260908032718-ecd99d761fe0. It is fixed in 2.11.1-0.20260908032718-ecd99d761fe0.
- How severe is CVE-2026-107218? CVE-2026-107218 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/xuri/excelize/v2 are affected by CVE-2026-107218? github.com/xuri/excelize/v2 (go) versions >= 2.10.1, < 2.11.1-0.20260908032718-ecd99d761fe0 is affected.
- Is there a fix for CVE-2026-107218? Yes. CVE-2026-107218 is fixed in 2.11.1-0.20260908032718-ecd99d761fe0. Upgrade to this version or later.
- Is CVE-2026-107218 exploitable, and should I be worried? Whether CVE-2026-107218 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-107218 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-107218? Upgrade
github.com/xuri/excelize/v2to 2.11.1-0.20260908032718-ecd99d761fe0 or later.