---
id: "CVE-2026-110676"
kind: "vulnerability"
aliases: ["CVE-2026-110676"]
title: "Cpanel::JSON::XS: crafted exponent numbers exhaust memory when re-encoded"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["cpanel-json-xs", "package", "perl", "web-services"]
not_affected_if: ["default-config", "no-bignum", "no-reencode"]
published_at: "2026-10-19T19:17:21+00:00"
first_seen_at: "2026-10-23T21:57:18+00:00"
updated_at: "2026-10-25T05:10:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-110676", "first_seen_at": "2026-10-23T21:57:18+00:00"}]
---

# Cpanel::JSON::XS: crafted exponent numbers exhaust memory when re-encoded

Cpanel::JSON::XS before 4.80 expands a JSON number with a large exponent into its full decimal form when it is encoded under allow_bignum. A 12-byte input such as [1e30000000] becomes about 30 MB, so untrusted input decoded and re-encoded can exhaust memory and CPU.

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

## How to check

- Check the installed version with `perl -MCpanel::JSON::XS -e 'print $Cpanel::JSON::XS::VERSION'`
- Search the codebase for `allow_bignum` and check whether decoded untrusted JSON is passed back to an encoder

## Fix

- Upgrade Cpanel::JSON::XS to `4.80` or later
- Until upgraded, do not re-encode untrusted JSON decoded with `allow_bignum`

## Timeline

- 2026-10-23T21:57:18+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-110676

## From the sources

Cpanel::JSON::XS versions before 4.80 for Perl allow memory exhaustion by encoding exponent notation as full decimal digits under allow_bignum.

With allow_bignum, a JSON number with a fraction or exponent decodes to a Math::BigFloat, which stores the exponent separately and so decodes cheaply. Encoding it untyped or as JSON_TYPE_FLOAT writes the plain decimal form with one digit per unit of exponent. Nothing bounds the exponent, so the 12-byte text [1e30000000] encodes to 30 MB.

Untrusted JSON decoded with allow_bignum and encoded again can exhaust memory and CPU.

---

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