Quick answers
- Is CVE-2026-103391 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-103391 being exploited in the wild.
- How severe is CVE-2026-103391?
- Medium severity, with a CVSS score of 5.3, published 28 October 2026.
- Which products and versions are affected?
- Juniper Networks Session Smart Router.
- Is there a fix for CVE-2026-103391?
- 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-2026-103391 attacked?
- It is attacked over the network, in a network appliance.
- Am I affected by CVE-2026-103391?
- Check whether you run Juniper Networks Session Smart Router. 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
An out-of-bounds write vulnerability exists in the SSR TCP proxy/optimization path when processing transit TCP packets with a crafted TCP option length field. The vulnerability can be exploited via a network-level attack requiring only a specially formed transit packet; no authentication or user interaction is needed. An attacker can corrupt packet data or trigger a data-plane crash.
Affected products
- Juniper Networks Session Smart Router
Timeline
- 2026-10-28: disclosed