Picotls has NULL pointer dereference during handshake, when running as a client
Only picotls used as a client-side TLS stack, at commits up to 44bc503, is affected. CVSS rates it 6.5 (medium); no vendor rating or fix is listed.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Picotls, a TLS protocol library used for client-side TLS connections, is affected. A malicious server can send crafted handshake messages that crash the client process, causing a denial of service that can also terminate other work running in that process.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original 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.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- h2o picotls
Version range not reported
References 3
GitHub · h2o/picotls
Questions about CVE-2026-59993
What does this mean?
When a peer sends a HelloRetryRequest followed by a spoofed Hello message, picotls can dereference a NULL pointer during the handshake. This may stop a process that uses picotls and is also doing other work, which is a denial of service.Source: github.com
Am I affected, and how do I check?
Affected revisions are picotls commits up to 44bc503, when picotls is used as the client-side TLS stack. Compare the picotls commit in use against 44bc503 and check whether it runs as a TLS client.Source: github.com
What should I do about it?
The checked facts do not list a fixed revision, so no upgrade target can be named. Watch the advisory for a fixed release.Source: github.com
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What if there's no patch?
The checked facts give no workaround. If possible, avoid using picotls as a client-side TLS stack until a fix is available.Source: github.com