Single-byte heap overwrite via scanf buffer growth
Published Apr 20, 2026 · Updated Apr 20, 2026
Heap buffer overflow in GNU Project glibc 2.7 through 2.43 allows attackers to write one byte past an allocated buffer via scanf input. The __vfscanf_internal buffer-growth formula subtracts one during realloc expansion for %mc, under-allocating the destination before the next byte is stored. Exploitation requires attacker-controlled input and a maximum width above 1024 that aligns with allocator chunk rounding; the demonstrated consequence is a controlled single-byte heap overwrite.
Summary
What happened
Heap buffer overflow in GNU Project glibc 2.7 through 2.43 allows attackers to write one byte past an allocated buffer via scanf input. The __vfscanf_internal buffer-growth formula subtracts one during realloc expansion for %mc, under-allocating the destination before the next byte is stored. Exploitation requires attacker-controlled input and a maximum width above 1024 that aligns with allocator chunk rounding; the demonstrated consequence is a controlled single-byte heap overwrite.
The record
- CVE
- CVE-2026-5450
- Published
- Apr 20, 2026
- Updated
- Apr 20, 2026
- Vendor
- The GnuPG Project
- Product
- glibc
- Classifications
- CWE-122, CWE-787, CAPEC-100
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 20, 2026CVE publishedPublication date reported by the CVE source.
- Apr 20, 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=2.7 <*
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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
- Upstream %1033mc minimal reproducerproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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