CVE-2026-59993
Medium
Description
Picotls is a TLS protocol library that allows users select different crypto backends based on their use case. In affected revisions through 44bc503, when picotls is used as a `client-side TLS stack`, a peer can send a `HelloRetryRequest` followed by a `spoofed Hello message` that causes a null-pointer dereference. This can terminate the consuming process, including a process performing other work, resulting in denial of service. This issue is fixed in commit a06ca41.
SeverityMedium
CVSS6.5
Exploit probability—
Product
H2o Picotls
PublishedOct 30, 2026
First seenNov 4, 2026
Weakness typeCWE-476NULL pointer dereference
How to fix
Sources list no fixed version or patch link for this vulnerability.
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| h2o picotls | < a06ca417a16f9126808bf5cabe6c5e6e0f16ecae | — |
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