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Technical How CVE-2026-49457 Works
CVE-2026-49457 is a critical vulnerability in the Erlang QUIC client implementation (erlang/quic) that completely breaks TLS 1.3 server authentication. During the TLS 1.3 handshake, the client fails to perform three essential security checks:
1. CertificateVerify signature not checked – The client does not verify the digital signature on the CertificateVerify message, which is supposed to prove that the server possesses the private key corresponding to its certificate.
2. Certificate chain not validated – The client does not validate the certificate chain against the trust store (cacerts option or operating system store).
3. Hostname not compared – The client does not check that the server’s certificate matches the hostname being connected to.
As a result, the `verify` configuration parameter was effectively a no-op – setting `verify => true` had absolutely no effect on the client’s behavior. A man-in-the-middle attacker positioned on the network path can present any certificate (including self-signed or maliciously crafted ones) and impersonate any server without detection. This defeats both the confidentiality and integrity of the QUIC connection.
HTTP/3, which uses the same QUIC client, is equally affected. Handshakes authenticated by a PSK (session resumption) are not affected, because the peer is authenticated by the PSK binder and no certificate is sent.
The vulnerability was fixed in version 1.4.4. The patch adds proper CertificateVerify signature verification, certificate chain validation against the trust store, and hostname comparison. The `verify` parameter now defaults to true; setting `verify => false` accepts any certificate (intended only for test environments with self-signed certificates).
No workarounds exist for versions before 1.4.4 – `verify => true` had no effect, and inspecting the certificate after connection does not help because without the signature check the peer is never proven to own the certificate it presents. The vulnerability was reported by benmmurphy.
DailyCVE Form:
Platform: Erlang/OTP
Version: <=1.4.3
Vulnerability: TLS cert bypass
Severity: Critical
date: 2026-07-01
Prediction: 2026-07-01
What Undercode Say:
Check erlang/quic version
In your rebar.config or mix.exs
{quic, "1.4.3"} VULNERABLE
Upgrade to fixed version
{quic, "1.4.4"} FIXED
Verify client configuration
Default in 1.4.4+:
verify => true Enables certificate validation
DO NOT use in production:
verify => false Accepts any certificate (test only)
Ensure cacerts is set or rely on OS store
cacerts => "/path/to/ca-bundle.crt"
Exploit:
A MITM attacker can exploit this vulnerability by:
- Positioning themselves on the network path between the QUIC client and the target server
2. Intercepting the TLS 1.3 handshake
- Presenting any certificate (e.g., a self-signed certificate or a certificate for a different domain)
- The client accepts it without validating the signature, chain, or hostname
- The attacker can then decrypt, read, and modify all QUIC/HTTP/3 traffic
No special tools are required – any standard TLS MITM proxy can present a certificate and successfully impersonate the target server.
Protection:
- Upgrade to erlang/quic version 1.4.4 or later immediately
- Verify that `verify => true` is set (default in 1.4.4+); do not set `verify => false` in production
- Ensure the `cacerts` option points to a valid CA trust store, or rely on the operating system’s default store
- Monitor for any clients still running versions <=1.4.3
- No workarounds exist for vulnerable versions – upgrading is the only solution
Impact:
- Confidentiality breach: MITM attackers can decrypt all QUIC/HTTP/3 traffic
- Integrity breach: Attackers can modify data in transit
- Impersonation: Attackers can present any certificate and impersonate any server
- Affected protocols: Both QUIC and HTTP/3 are vulnerable
- PSK sessions: Not affected (session resumption uses PSK binder authentication)
- CVSS Score: Critical severity
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Sources:
Reported By: github.com
Extra Source Hub:
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