Integer Underflow Affecting rust-rustls-webpki package, versions *


Severity

Recommended
0.0
high
0
10

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Threat Intelligence

EPSS
0.35% (29th percentile)

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  • Snyk IDSNYK-ECHOLATEST-RUSTRUSTLSWEBPKI-19946244
  • published19 Sept 2026
  • disclosed18 Sept 2026

Introduced: 18 Sep 2026

NewCVE-2026-93599  (opens in a new tab)
CWE-191  (opens in a new tab)

How to fix?

There is no fixed version for Echo:latest rust-rustls-webpki.

NVD Description

Note: Versions mentioned in the description apply only to the upstream rust-rustls-webpki package and not the rust-rustls-webpki package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1