Memory corruption via bc_str2num buffer underallocation
Published Jul 30, 2026 · Updated Jul 30, 2026
Out-of-bounds write in PHP 8.4.0 through 8.4.23 and 8.5.0 through 8.5.8 allows remote attackers to corrupt memory via bccomp(). In bc_str2num(), trailing-zero trimming reduces the allocated fractional length without moving fractional_end, so a later copy writes the original fraction into an undersized buffer. Reachability requires an application to pass attacker-controlled numeric operands and a truncating scale to BCMath; the overwrite can corrupt stack or heap memory.
Summary
What happened
Out-of-bounds write in PHP 8.4.0 through 8.4.23 and 8.5.0 through 8.5.8 allows remote attackers to corrupt memory via bccomp(). In bc_str2num(), trailing-zero trimming reduces the allocated fractional length without moving fractional_end, so a later copy writes the original fraction into an undersized buffer. Reachability requires an application to pass attacker-controlled numeric operands and a truncating scale to BCMath; the overwrite can corrupt stack or heap memory.
The record
- CVE
- CVE-2026-17544
- Published
- Jul 30, 2026
- Updated
- Jul 30, 2026
- Vendor
- The PHP Group
- Product
- PHP
- Classifications
- CWE-121, CWE-787, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 30, 2026CVE publishedPublication date reported by the CVE source.
- Jul 30, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=8.4.* <8.4.24
- Affected versionversion=8.5.* <8.5.9
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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