# CVE-2026-35191: OpenSSL QUIC packet credit miscounting in non-validation mode

Source: https://junglewise.ai/threats/cve-2026-35191-issue-summary-the-openssl-quic-server-when-configured-to-not  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-35191 · Severity: info · Published 2026-09-29

OpenSSL's QUIC server implementation, when address validation is disabled, miscounts incoming packets when multiple packets arrive in a single datagram. This allows an attacker to manipulate the server's amplification limit calculations, potentially using the server as a relay to amplify denial-of-service attacks against third parties.

Technologies: [OpenSSL](https://junglewise.ai/threats/technologies/openssl). Vendors: [OpenSSL](https://junglewise.ai/threats/vendors/openssl).

## Quick answers

**Is CVE-2026-35191 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-35191 being exploited in the wild.

**How severe is CVE-2026-35191?** Informational severity, published 29 September 2026.

**Which products and versions are affected?** OpenSSL <UNKNOWN>.

**Is there a fix for CVE-2026-35191?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-35191 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-35191?** Check whether you run OpenSSL at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

When the QUIC server operates without address validation (non-validation mode), it charges the entire datagram length against the unvalidated credit limit for each QUIC packet contained in that datagram, rather than once per datagram. An attacker can craft a single datagram containing multiple QUIC packets to artificially inflate the server's perception of received data, bypassing the RFC 9000-mandated 3x amplification limit until TLS handshake completion. This is a violation of expected behavior under RFC 9000 Section 8.

## Affected products

- OpenSSL OpenSSL <UNKNOWN>

## Timeline

- 2026-09-29: disclosed

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