External risk intelligence

Erlang QUIC and HTTP/3 TLS Handshake Certificate Verification Failure

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-49457

This vulnerability exists in a client-side library (erlang_quic) used to initiate QUIC and HTTP/3 connections. It affects the client's ability to verify server certificates. As a client-side component, it is not a listener or service exposed to the public internet, but rather a dependency used by applications to connect to external servers.

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

The `erlang_quic` and HTTP/3 client libraries contained a critical flaw where they did not properly authenticate servers during the TLS handshake. This allowed attackers to impersonate any server, potentially compromising the confidentiality and integrity of network connections. The issue is resolved in version 1.4.4.

Issue: Client did not verify server identity.
Why remember: Protects connection confidentiality and integrity.
Takeaway: Ensure server authentication is enforced.

Attack Path

How an attacker could exploit the issue

An attacker on the network path could impersonate any server to a vulnerable client, intercepting all traffic and potentially altering it. This is possible because the QUIC and HTTP/3 client improperly handles TLS 1.3 handshakes, failing to verify the server's presented certificate. This allows an attacker to establish a connection with the client, posing as a legitimate server, and compromise the confidentiality and integrity of the communication.

Network access needed.
Client TLS handshake does not verify server.
Confidentiality and integrity at risk.

Live Threat

Current exploitation, exposure, and threat context

The QUIC client in erlang_quic, prior to version 1.4.4, failed to authenticate servers during the TLS 1.3 handshake. This allowed a network attacker to impersonate any server, compromising the confidentiality and integrity of the connection, unless the connection was authenticated by a pre-shared key (PSK).

Connection confidentiality and integrity.
Man-in-the-middle can impersonate servers.
Compromised connection data.

Operational Fix

Recommended remediation, mitigation, and detection steps

To address this vulnerability, the teams responsible for applications utilizing the erlang_quic library for QUIC and HTTP/3 connections should take the lead. The first practical step is to identify all instances where this library is employed, determine if these connections are business-critical, and then confirm the specific application or service owner accountable for its management. Planning remediation efforts should then be based on the identified risk and ownership.

Application owners should manage this issue.
Verify client implementation reachability and criticality.
Plan and coordinate remediation actions.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

Free EASM Trial See How Signal Works

Frequently asked questions

What is erlang_quic and how is it used?

erlang_quic is a library written in Erlang that provides an implementation of the QUIC network protocol. Developers use it to enable QUIC or HTTP/3 communication capabilities within their Erlang applications, allowing those applications to connect to other systems or services that support these high-performance transport protocols.

How does CVE-2026-49457 affect TLS connections?

This vulnerability falls under Improper Certificate Validation. It means the software fails to verify the identity of the server it is connecting to during a TLS 1.3 handshake. Because the library ignores signature checks and hostnames, it cannot distinguish between a legitimate server and an attacker posing as one, which breaks the security guarantees of the connection.

Do I need to worry if my connection uses a pre-shared key?

No. If your connection is authenticated using a pre-shared key (PSK) during session resumption, you are not affected. In this specific scenario, the peer is authenticated via the PSK binder rather than a certificate, meaning the vulnerable certificate verification logic is bypassed entirely.

Is my server at risk because of this CVE?

Halo Surface Signal indicates this is a client-side library issue, not a server-side listener. Because the vulnerability resides in the code that initiates connections, the risk is not about your server being exposed to the public internet, but rather whether your internal applications are connecting to untrusted or malicious destinations.

How do I fix the erlang_quic vulnerability?

The only way to resolve this is to update the library to version 1.4.4 or later. Once updated, the client will properly validate certificate chains and hostnames by default. You should identify which of your applications depend on this library, coordinate with the respective owners, and prioritize upgrading these components to ensure proper server authentication is enforced.

References

github.com/benoitc/erlang_quic/security/advisories/GHSA-2r8v-p65…

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.