CVE-2026-103391VulnerabilityPublished 28 Oct 2026

Juniper Networks Session Smart Router · Out-of-bounds Write Vulnerability

Source GCVE Database

Authoritative record:CVE-2026-103391· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium · fixed in 7.2.3 : update Session Smart Router when convenient.

Data as of 28 Oct 2026, 20:01 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 7.2.3, 7.1.7, 7.0.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-mg4c-h4g5-47fv

What to do

Upgrade Session Smart Router to 7.2.3, 7.1.7 or 7.0.5.

Affected software

Product	Affected	Fixed in
Juniper NetworksSession Smart Router	Affected >=7.2.0 <7.2.3	Fixed in 7.2.3
Juniper NetworksSession Smart Router	Affected >=7.1.0 <7.1.7	Fixed in 7.1.7
Juniper NetworksSession Smart Router	Affected <7.0.5	Fixed in 7.0.5

AI-suggested

No specific mitigation or workaround is provided in the available data.

Description

An out-of-bounds write vulnerability exists in the TCP proxy/optimization path of Juniper Networks Session Smart Router. This flaw allows an attacker to corrupt forwarded packet data and may cause a data-plane crash when a specially crafted TCP packet with an invalid TCP option length is processed. The vulnerability has a medium severity rating with a CVSS score of 5.3.

Impact

An attacker can send specially crafted TCP packets to the affected router, causing corruption of forwarded packet data and potentially triggering a data-plane crash. This may disrupt network traffic passing through the router but does not directly impact confidentiality. The vulnerability has a medium severity level (CVSS 5.3) with no known exploitation in the wild.

Summary

CVE-2026-103391 describes an out-of-bounds write vulnerability in the SSR TCP proxy/optimization path of Juniper Networks Session Smart Router. The issue arises from improper handling of transit TCP packets containing crafted TCP option lengths, which can lead to corruption of forwarded packet data and potentially cause a crash of the data plane. The vulnerability does not require privileges or user interaction and has a network attack vector.

CWE-787Out-of-bounds Write (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #5
The product writes data past the end, or before the beginning, of the intended buffer.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Oct 2026, 20:01 UTC

WeaknessesCWE-787

Technical details

References

Community reviews

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