One-byte heap overwrite via DER length miscalculation
Published Aug 22, 2026 · Updated Aug 22, 2026
Heap-based buffer overflow in OpenWrt LuCI openwrt-18.06 through openwrt-25.12 allows local users to overwrite one heap byte. In asn1_add_obj, allocation uses the DER length of a 255-byte signature, while encoding adds an unused-bits byte and emits the larger 256-byte length before memcpy writes 255 bytes. Low-privileged local access to create_selfsigned() is required; the demonstrated consequence is an out-of-bounds write, and remote reachability depends on the embedding application.
Summary
What happened
Heap-based buffer overflow in OpenWrt LuCI openwrt-18.06 through openwrt-25.12 allows local users to overwrite one heap byte. In asn1_add_obj, allocation uses the DER length of a 255-byte signature, while encoding adds an unused-bits byte and emits the larger 256-byte length before memcpy writes 255 bytes. Low-privileged local access to create_selfsigned() is required; the demonstrated consequence is an out-of-bounds write, and remote reachability depends on the embedding application.
The record
- CVE
- CVE-2026-62381
- Published
- Aug 22, 2026
- Updated
- Aug 22, 2026
- Vendor
- OpenWrt
- Product
- LuCI
- Classifications
- CWE-122
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 22, 2026CVE publishedPublication date reported by the CVE source.
- Aug 22, 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?
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- Affected versionversion=0 <=42d72f79cd8f057f241595abc761b39dab2d9f07
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
- GHSA-jgc3-4q3p-g6xh AddressSanitizer reproductionproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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