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PPPD memory corruption and crash triggerable by EAP-TLS authenticated peer

Moderate
paulusmack published GHSA-cgh4-298h-6g7q Sep 15, 2026

Package

PPP

Affected versions

2.4.9 to 2.5.3

Patched versions

2.5.4

Description

Impact

A PPP peer system that authenticates itself to pppd using the EAP-TLS protocol can, by sending an extra EAP-TLS Ack packet after the end of the authentication sequence, trigger the use of memory that has been freed (UAF) in pppd, followed by an attempt by pppd to free that memory again. The result is memory corruption in pppd, which runs as root, generally followed by the pppd process aborting when the double free is detected. This denies service to that peer but does not impact any other PPP connection, because each pppd process only serves one peer.

The extra EAP-TLS Ack packet is not something that a correct EAP-TLS implementation would send; the peer would have to be malicious or buggy. The peer would need to have a certificate signed by a CA recognized by the local pppd and be able to authenticate itself using that certificate.

Patches

PR #625 fixes it via the commit "pppd/EAP-TLS: Fix use-after-free bug in eapTlsRecvClient state". This patch is in v2.5.4.

Workarounds

Don't use EAP-TLS authentication for any untrusted peer.

References

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVE ID

No known CVE

Weaknesses

No CWEs

Credits