---
title: "CVE-2026-93599: rustls-webpki - Denial of Service"
description: "rustls-webpki <= 0.103.12 and 0.104.0-alpha < 0.104.0-alpha.7 contain a denial of service caused by an underflow panic in bit_string_flags() when parsing a crafted CRL with an issuingDistributionPoint extension, letting attackers cause a panic via crafted CRL input, exploit requires explicit CRL revocation checking enabled and attacker-controlled CRL bytes."
url: https://panop.io/threat-heartbeat/CVE-2026-93599/
---

# CVE-2026-93599 rustls-webpki - Denial of Service

rustls-webpki <= 0.103.12 and 0.104.0-alpha < 0.104.0-alpha.7 contain a denial of service caused by an underflow panic in bit\_string\_flags() when parsing a crafted CRL with an issuingDistributionPoint extension, letting attackers cause a panic via crafted CRL input, exploit requires explicit CRL revocation checking enabled and attacker-controlled CRL bytes.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

EPSS

0.35% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-93599)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

18 September 2026

Updated

15 October 2026

Weakness

[CWE-191](https://cwe.mitre.org/data/definitions/191.html)

## Vendor fix

Upgrade to version 0.103.13 or 0.104.0-alpha.7 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-93599](https://nvd.nist.gov/vuln/detail/CVE-2026-93599)
- [https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8](https://github.com/rustls/webpki/security/advisories/GHSA-82j2-j2ch-gfr8)
- [https://www.vulncheck.com/advisories/rustls-webpki-before-0.103.13-panic-via-empty-bit-string](https://www.vulncheck.com/advisories/rustls-webpki-before-0.103.13-panic-via-empty-bit-string)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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