CVE-2026-6103: Integer Overflow (CVSS 4.3)

Description

phar_tar_number() parses the octal size field of a TAR header into a uint32_t with no overflow check. The field is 11 octal digits wide and holds values up to 0x1FFFFFFFF, so a size above 0xFFFFFFFF silently wraps. The parser then skips the wrong number of data blocks and interprets attacker-controlled file content as the next TAR header, which lets a crafted archive inject entries that PharData reports and extracts as if they were genuine.

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CVSS v3.1 Score

4.3

MEDIUM

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

EPSS — Exploit Prediction

0.0017

Probability of exploitation

0.05%

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-190 Integer Overflow

References

Other References

https://github.com/php/php-src/security/advisories/GHSA-j3wh-g957-2m85 https://github.com/php/php-src/security/advisories/GHSA-j3wh-g957-2m85

Frequently Asked Questions

What is CVE-2026-6103? +

phar_tar_number() parses the octal size field of a TAR header into a uint32_t with no overflow check. The field is 11 octal digits wide and holds values up to 0x1FFFFFFFF, so a size above 0xFFFFFFFF silently wraps. The parser then skips the wrong number of data blocks and interprets attacker-controlled file content as the next TAR header, which lets a crafted archive inject entries that PharData reports and extracts as if they were genuine. It has a CVSS v3.1 base score of 4.3 (MEDIUM).

How severe is CVE-2026-6103? +

CVE-2026-6103 has a CVSS v3.1 score of 4.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0017, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-6103? +

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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