---
id: "CVE-2026-110688"
kind: "vulnerability"
aliases: ["CVE-2026-110688"]
title: "Cpanel::JSON::XS: incremental parser lets a peer burn CPU with non-ASCII JSON"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["cpanel-json-xs", "network-services", "package", "perl"]
not_affected_if: ["no-incr-parse", "trusted-input-only", "version-outside-4.51-4.79"]
published_at: "2026-10-19T19:17:22+00:00"
first_seen_at: "2026-10-23T21:57:18+00:00"
updated_at: "2026-10-25T05:10:42+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110688", "first_seen_at": "2026-10-23T21:57:18+00:00"}]
---

# Cpanel::JSON::XS: incremental parser lets a peer burn CPU with non-ASCII JSON

Cpanel::JSON::XS versions 4.51 through 4.79 for Perl re-validate the rest of the input buffer for every value when incr_parse meets non-ASCII text, so CPU use grows with the square of the input size. A remote peer sending about a megabyte of ordinary non-ASCII JSON in one read can tie up the process for seconds, a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `perl -MCpanel::JSON::XS -e 'print $Cpanel::JSON::XS::VERSION'` to read the installed version
- Search lockfiles and `cpanfile.snapshot` for `Cpanel::JSON::XS` and check whether the version falls between 4.51 and 4.79
- Check whether the application calls `incr_parse` on data read from the network

## Fix

- Upgrade Cpanel::JSON::XS to `4.80` or later
- Rebuild and redeploy Perl services that bundle the module

## Timeline

- 2026-10-23T21:57:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-110688

## From the sources

Cpanel::JSON::XS versions from 4.51 before 4.80 for Perl allow quadratic CPU use by revalidating the remaining buffer per value in incr_parse.

At the first non-ASCII byte in a string, the decoder validates UTF-8 from there to the end of its input. incr_parse decodes each buffered value with a fresh decoder, so every value revalidates the rest of the buffer, and doubling the input quadruples the work.

A peer that sends about a megabyte of ordinary non-ASCII JSON in one read ties up the process for seconds of CPU time.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_