CVE-2026-67216: cjson — Exploit & Fix

Description

cJSON through 1.7.19 contains an inefficient algorithmic complexity flaw in cJSON_Compare(). When comparing objects, the function recurses into each shared subtree twice, once in each direction, with no depth guard, making the running time exponential in nesting depth. A small, deeply nested document of a few hundred bytes (depth around 40) compared for equality consumes hours of CPU, and the cost roughly doubles with each additional level of nesting. An application that calls cJSON_Compare() on attacker-influenced JSON that is structurally equal to a reference document is exposed to a denial-of-service condition.

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CVSS v3.1 Score

5.9

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0043

Probability of exploitation

0.35%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-407 CWE-407

Affected Products

Vendor	Product	Versions
davegamble	cjson	< 1.7.19

References

Advisories & Patches

https://github.com/DaveGamble/cJSON/blob/v1.7.19/cJSON.c#L3057-L3180

Exploits

https://joshua.hu/cjson-json-parser-cve-vulnerabilities

Other References

https://www.vulncheck.com/advisories/cjson-cjson-compare-exponential-complexity-denial-of-service

Frequently Asked Questions

What is CVE-2026-67216? +

cJSON through 1.7.19 contains an inefficient algorithmic complexity flaw in cJSON_Compare(). When comparing objects, the function recurses into each shared subtree twice, once in each direction, with no depth guard, making the running time exponential in nesting depth. A small, deeply nested document of a few hundred bytes (depth around 40) compared for equality consumes hours of CPU, and the cost roughly doubles with each additional level of nesting. An application that calls cJSON_Compare() on attacker-influenced JSON that is structurally equal to a reference document is exposed to a denial-of-service condition. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-67216? +

CVE-2026-67216 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0043, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-67216? +

CVE-2026-67216 affects products from davegamble, specifically: cjson. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-67216? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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