CVE-2026-129483
Received Received - Intake

Authentication Bypass in Cyrus SASL via SRP Mechanism

Publication date: 2026-11-15

Last updated on: 2026-11-15

Assigner: VulnCheck

Description
Cyrus SASL through 2.1.28 contains an authentication bypass vulnerability in the SRP server mechanism because srp_server_mech_step2 does not reject client public values A that are multiples of N. Unauthenticated network clients can send A equal to N to force a zero shared secret, authenticating as any existing user without the password and learning session keys.

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Meta Information

Published
2026-11-15
Last Modified
2026-11-15
Generated
2026-11-15
AI Q&A
2026-11-15
EPSS Evaluated
N/A
NVD
CVE-2026-129483
EUVD
EUVD-2026-126032

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
cyrusimap cyrus-sasl From 0 (inc) to 2.1.28 (inc)

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-287 When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

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Executive Summary

CVE-2026-129483 is an authentication bypass flaw in Cyrus SASL's SRP server mechanism. An unauthenticated attacker can send a crafted public value A equal to N (a multiple of N) during the SRP handshake. The server fails to reject this value, causing the shared secret to become zero. This allows the attacker to authenticate as any existing user without a password and learn session keys.

Detection Guidance

To detect this vulnerability, check if Cyrus SASL 2.1.28 or the master branch with SRP enabled is running. Use commands like 'saslauthd -v' or 'ldd /usr/lib/libsasl2.so | grep srp' to verify SRP plugin presence. Monitor network traffic for SRP handshake attempts where client public value A equals N or is a multiple of N.

Impact Analysis

This vulnerability allows unauthenticated attackers to gain unauthorized access to systems using Cyrus SASL with SRP enabled. They can impersonate any user, bypass authentication, and potentially steal sensitive data or session keys. Systems relying on Cyrus SASL for authentication are at high risk of compromise.

Compliance Impact

This vulnerability can lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations using affected systems may face compliance failures, legal penalties, and reputational damage due to data breaches resulting from the authentication bypass.

Mitigation Strategies

Immediately disable the SRP mechanism in Cyrus SASL by recompiling without --enable-srp or upgrading to a patched version. If upgrading is not possible, apply the fix from the upstream commit removing SRP support (fb3724f). Block external access to SASL services until mitigation is complete.

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