# CVE-2026-45271: picotls has infinite recursion in the minicrypto ASN.1 decoder

> An attacker can crash applications using the minicrypto backend by supplying a deeply nested ASN.1 structure in a private key file.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 21 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-84f5-m5x2-82q4

## What is CVE-2026-45271?

CVE-2026-45271 is a medium-severity denial of service vulnerability in h2o picotls, published on 21 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

Picotls is a TLS protocol library that allows users select different crypto backends based on their use case. Picotls implements its own ASN.1 validation helper, which is used by the minicrypto backend while parsing local PKCS#8 private keys. Prior to commit c14231d801407640bc42c2dcf92783409ea6a7c7, the validator recursively descends into constructed ASN.1 elements without enforcing a maximum nesting depth. If an application loads an attacker-supplied private-key file through ptls_minicrypto_load_private_key(), or otherwise calls the public ASN.1 validation API on untrusted DER, a crafted deeply nested ASN.1 structure can exhaust the process stack and crash the application. Note that the libcrypto (OpenSSL) backend does not use the ASN.1 validation helper of picotls, and therefore is immune to this vulnerability. The vulnerability has been addressed in commit c14231d801407640bc42c2dcf92783409ea6a7c7.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-45271?


## How do I fix CVE-2026-45271?

No fix has been published for CVE-2026-45271 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45271 being exploited?

There is no known exploitation of CVE-2026-45271 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45271 and fix it if it is affected.

What it is: CVE-2026-45271 is a medium-severity denial of service vulnerability in h2o picotls, published on 21 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-45271 in the wild and no public exploit code.

Affected product: h2o picotls. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45271/ (Markdown: https://insights.sbomify.com/CVE-2026-45271/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45271
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45271
- OSV: https://osv.dev/vulnerability/CVE-2026-45271

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-45271/
Summaries are generated and may contain mistakes; the official description above is the record.