# CVE-2026-103392: Juniper Networks Session Smart Router TCP out-of-bounds write

Source: https://junglewise.ai/threats/cve-2026-103392-an-out-of-bounds-write-vulnerability-in-the-tcp-header  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-28. Updated: 2026-10-28  
License: CC BY 4.0 with a link back

CVE-2026-103392 · Severity: medium · CVSS 4.8 · Published 2026-10-28

Juniper Networks Session Smart Router is a network router that processes traffic between corporate sites. An attacker can send a specially crafted TCP packet with an oversized SACK option to corrupt payload data and disrupt active sessions, potentially causing network outages or data loss.

Technologies: [Juniper Networks Session Smart Router](https://junglewise.ai/threats/technologies/session-smart-router). Vendors: [Juniper Networks](https://junglewise.ai/threats/vendors/juniper-networks).

## Quick answers

**Is CVE-2026-103392 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-103392 being exploited in the wild.

**How severe is CVE-2026-103392?** Medium severity, with a CVSS score of 4.8, published 28 October 2026.

**Which products and versions are affected?** Juniper Networks Session Smart Router.

**Is there a fix for CVE-2026-103392?** 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-2026-103392 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-103392?** 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 TCP header processing when handling SACK (Selective Acknowledgment) options with oversized length fields. An unauthenticated attacker on the network can send a malicious transit TCP packet to trigger the flaw, corrupting TCP payload data and causing session desynchronization. No authentication or user interaction is required.

## Affected products

- Juniper Networks Session Smart Router

## Timeline

- 2026-10-28: disclosed

## References

- [https://supportportal.juniper.net/JSA112183](https://supportportal.juniper.net/JSA112183)

## Related threats

- [Juniper Session Smart Router OS command injection in AccessManager](https://junglewise.ai/threats/cve-2026-106079-an-improper-neutralization-of-special-elements-used-in-an-os)
- [Juniper Networks Session Smart Router integer underflow in DHCP decoder](https://junglewise.ai/threats/cve-2026-103411-an-integer-underflow-vulnerability-in-dhcpmessagedecoder-in)
- [Juniper Networks Session Smart Router integer overflow in DPI certificate scanner](https://junglewise.ai/threats/cve-2026-103410-an-integer-overflow-vulnerability-in-the-dpi-certificate-scanner)
- [Juniper Networks Session Smart Router missing authentication](https://junglewise.ai/threats/cve-2026-103409-a-missing-authentication-for-critical-function-vulnerability-in)
- [Juniper Networks Session Smart Router stack buffer overflow in DHCP client](https://junglewise.ai/threats/cve-2026-103408-a-stack-buffer-overflow-vulnerability-in-the-dhcp-client-in)