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CVE-2026-17544 is an out-of-bounds write vulnerability in PHP’s BCMath extension, affecting the bccomp() function in PHP 8.4.x before 8.4.24 and 8.5.x before 8.5.9. The flaw is triggered when an application passes attacker-controlled numeric strings together with a specific scale value to bccomp(). The vulnerable condition is in bc_str2num(), where fractional digits are truncated and trailing zeroes are removed. During that processing, the implementation reduces the allocated buffer size but fails to update the pointer marking the end of the copied fractional data, creating a mismatch between the copied data and the allocated buffer. This can result in an out-of-bounds write and consequent stack or heap memory corruption.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
8 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A high-severity out-of-bounds write vulnerability in PHP's BCMath extension affecting bccomp(), caused by incorrect buffer/end-pointer handling in bc_str2num() after truncating fractional digits and trailing zeroes.
An out-of-bounds write vulnerability in PHP's ext-bcmath bccomp() function that can cause stack and heap corruption.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.