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Improper Input ValidationWeakness · CWE-20

CVE-2026-42327

HIGH · 8.7 CVSS v4.0 Published 2026-05-14
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
96/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
rust-openssl provides OpenSSL bindings for the Rust programming language. From 0.9.7 to before 0.10.79, X509Ref::ocsp_responders returns OCSP responder URLs from a certificate's AIA extension as OpensslString, whose Deref<Target = str> wraps the raw bytes with str::from_utf8_unchecked. OpenSSL does not enforce that the underlying IA5String is ASCII, so a certificate with non-UTF-8 bytes in its OCSP accessLocation causes safe Rust code to construct a &str that violates the UTF-8 invariant — resulting in undefined behavior. This vulnerability is fixed in 0.10.79.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In rust-openssl versions 0.9.7 through 0.10.78, the X509Ref::ocsp_responders method returns OCSP responder URLs from the AIA extension as OpensslString, which uses str::from_utf8_unchecked to wrap raw bytes. Since OpenSSL's IA5String doesn't enforce ASCII compliance, a malicious certificate containing non-UTF-8 bytes in the OCSP accessLocation field causes safe Rust code to construct an invalid &str, violating Rust's UTF-8 invariant and triggering undefined behavior.

MitigationUpgrade rust-openssl to version 0.10.79 or later. If upgrade is not immediately feasible, audit code using X509Ref::ocsp_responders for potential crashes or memory corruption, and consider validating OCSP responder strings before use.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check rust-openssl version in your dependencies
    Inspect your Cargo.lock file for the rust-openssl entry, or run 'cargo tree -p rust-openssl' to see the installed version
    Affected if The version listed is 0.9.7 through 0.10.78 (inclusive)
  2. Verify X509Ref::ocsp_responders is called in your codebase
    Search your source code for occurrences of 'ocsp_responders' method calls on X509Ref or similar certificate types
    Affected if The method is called and processes certificates from untrusted or external sources
  3. Identify if your application processes external certificates
    Review code paths that load or parse X.509 certificates, particularly those from network connections, TLS handshakes, or user-provided files
    Affected if Certificates from untrusted sources are parsed using the affected method
  4. Check for OCSP/ AIA extension processing
    Search for code that accesses certificate AIA (Authority Information Access) extensions or OCSP responder URLs
    Affected if Your code explicitly reads OCSP responder URLs from certificate AIA extensions

You are affected if rust-openssl version 0.9.7-0.10.78 is in use AND your code calls X509Ref::ocsp_responders to process certificates from untrusted or external sources.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade rust-openssl to version 0.10.79 or later. If upgrade is not immediately feasible, audit code using X509Ref::ocsp_responders for potential crashes or memory corruption, and consider validating OCSP responder strings before use.

Recommended fix High confidence

rust-openssl version 0.10.79

  1. Update the rust-openssl dependency in your Cargo.toml to version 0.10.79 or later
  2. Run `cargo update` or `cargo build` to fetch the updated crate
  3. Verify the update was successful by checking the resolved version with `cargo tree | grep openssl`
  4. Rebuild your project to ensure the vulnerability is patched

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,600
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42327 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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