What is CVE-2026-17544?

CVE-2026-17544 is a critical-severity vulnerability in PHP, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-07-30.

How severe is CVE-2026-17544?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2026-17544 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in PHP

CVE-2026-17544

Attacker-provided inputs to bccomp() could lead to an out-of-bounds write with stack and heap corruption in PHP versions from 8.4.* before 8.4.24 and from 8.5.* before 8.5.9.

Vulnerability class: Buffer Overflow

Published 2026-07-30 · last modified 2026-10-23.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (36.0th percentile), scored 2026-10-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 36.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: -0.000

Affected products

PHP
PHP Group — versions 8.4.*, 8.5.*

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

Public proof-of-concept exploits

References

github.com/php/php-src/security/advisories/GHSA-x692-q9x7-8c3f (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-17544?: CVE-2026-17544 is a critical-severity vulnerability in PHP, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-07-30.
How severe is CVE-2026-17544?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2026-17544 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.