---
id: CVE-2026-93599
title: >-
  rustls-webpki through 0.103.12 (and 0.104.0-alpha releases before
  0.104.0-alpha.7) contains a reachable panic in bit_string_flags() in
  src/der.rs
summary: >-
  rustls-webpki through 0.103.12 (and 0.104.0-alpha releases before
  0.104.0-alpha.7) contains a reachable panic in bit_string_flags() in
  src/der.rs. The input guard fails to reject a named-bit BIT STRING whose
  content is exactly [0x00] (ze…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-191
  - CWE-125
vendor: rustls
product: webpki
affected:
  - webpki < 0.103.13
  - webpki >= 0.104.0-alpha.1 < 0.104.0-alpha.7
patched:
  - rustls-webpki 0.104.0-alpha.7
published: '2026-09-18'
updated: '2026-09-22'
sourceUpdated: '2026-09-22T20:25:55.870'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-93599'
references:
  - url: 'https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/rustls-webpki-before-0.103.13-panic-via-empty-bit-string
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://crates.io/crates/rustls-webpki'
  - url: 'https://rustsec.org/advisories/RUSTSEC-2026-0104.html'
  - url: 'https://github.com/rustls/webpki'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93599.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-93599'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2538431'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-93599'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-93599'
  - url: 'https://access.redhat.com/errata/RHSA-2026:56999'
  - url: 'https://access.redhat.com/errata/RHSA-2026:66076'
  - url: 'https://access.redhat.com/errata/RHSA-2026:42825'
  - url: 'https://access.redhat.com/errata/RHSA-2026:57200'
  - url: 'https://access.redhat.com/errata/RHSA-2026:70694'
tags:
  - nvd
  - cve.org
  - exploit-available
  - osv
  - rust
  - csaf
  - vex
  - red-hat
epss: 0.00488
epssPercentile: 0.39425
aliases:
  - RUSTSEC-2026-0104
  - GHSA-82j2-j2ch-gfr8
ecosystem: rust
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-18T14:04:54.272751Z'
ingestedAt: '2026-09-18T13:41:41.663Z'
---

## Overview

rustls-webpki through 0.103.12 (and 0.104.0-alpha releases before 0.104.0-alpha.7) contains a reachable panic in bit_string_flags() in src/der.rs. The input guard fails to reject a named-bit BIT STRING whose content is exactly [0x00] (zero padding bits and no data bytes), so raw_bits.len() - 1 underflows on the empty slice and the subsequent index operation panics (subtract-with-overflow in debug, index-out-of-bounds in release). The condition is reachable through the public API BorrowedCertRevocationList::from_der() when a CRL contains an issuingDistributionPoint extension with such an onlySomeReasons value. Exploitation requires an application that explicitly opts in to CRL revocation checking by passing RevocationOptions to verify_for_usage() and that parses CRL bytes obtained from a source the attacker can influence; the default rustls configuration, which does not use RevocationOptions, is unaffected. A crafted CRL causes a denial of service via the panic. Fixed in 0.103.13 and 0.104.0-alpha.7.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-93599)

Affected packages:

- `rustls-webpki >= 0.104.0-alpha.1, < 0.104.0-alpha.7`

Patched in:

- `rustls-webpki 0.104.0-alpha.7`

Source: https://osv.dev/vulnerability/RUSTSEC-2026-0104

## Vendor advisories

- **Red Hat VEX** · Important · affected: Ansible Automation Orchestrator 2026, Confidential Cluster Operator, Logging Subsystem for Red Hat OpenShift, Migration Toolkit for Applications 8, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, … · no fix planned: OpenShift Lightspeed, Red Hat Ansible Automation Platform 2, Red Hat Trusted Profile Analyzer, Ansible Automation Orchestrator 2026, … · updated 2026-09-25 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-93599.json)
- **RHSA-2026:56999** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-19 · [advisory](https://access.redhat.com/errata/RHSA-2026:56999)
- **RHSA-2026:66076** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:66076)
- **RHSA-2026:42825** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-07-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:42825)
- **RHSA-2026:57200** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:57200)
- **RHSA-2026:70694** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70694)