VulnerabilityPublished 15 Jan 2026

CVE-2026-21906: Juniper Networks Junos OS · Improper Handling of Exceptional Conditions

Affects Juniper Networks Junos OSSource CVE Database V5

Not known to be exploited · CVSS 7.5 High · fixed in 25.2R1-S1 : patch Juniper Networks Junos OS soon.

Data as of 26 Oct 2026, 12:55 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 45% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 25.2R1-S1, 24.4R2-S1, 24.2R2-S3 +4

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

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

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: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 15 Jan 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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
Juniper NetworksJunos OS	Affected <21.4R3-S12 >=22.4 <22.4R3-S8 >=23.2 <23.2R2-S5 >=23.4 <23.4R2-S5 >=24.2 <24.2R2-S3 >=24.4 <24.4R2-S1 =25.2	Fixed in 25.2R1-S1 24.4R2-S1 24.2R2-S3 23.4R2-S5 23.2R2-S5 22.4R3-S8 21.4R3-S12

AI-suggested

European organizations should immediately audit their Juniper SRX Series devices to identify affected Junos OS versions and verify if GRE performance acceleration is enabled alongside PMI. Since PMI is enabled by default, special attention should be given to GRE acceleration settings. If you cannot patch yet, consider disabling GRE performance acceleration if feasible to reduce exposure. Network administrators should implement monitoring for unusual ICMP traffic patterns, especially ICMP packets traversing GRE tunnels, and apply rate limiting or filtering where appropriate. Deploying intrusion detection/prevention systems (IDS/IPS) with signatures targeting anomalous ICMP GRE traffic may help detect exploitation attempts. Additionally, network segmentation and strict access controls on management and data plane interfaces can limit exposure. Regularly reviewing vendor advisories and subscribing to Juniper security notifications will ensure timely awareness of updates.

Description

CVE-2026-21906 is a high-severity vulnerability in Juniper Networks Junos OS running on SRX Series devices. It involves improper handling of exceptional conditions in the packet forwarding engine (PFE) when processing a specific ICMP packet sent through a GRE tunnel with PowerMode IPsec (PMI) and GRE performance acceleration enabled. An unauthenticated attacker can exploit this remotely to cause the PFE to crash and restart, resulting in traffic loss and potential denial of service. PMI is enabled by default, and GRE performance acceleration is configurable on certain SRX platforms, increasing exposure. The vulnerability affects multiple Junos OS versions prior to specific patched releases. Although no exploits are currently known in the wild, the ease of network-based exploitation without authentication makes this a significant risk for organizations using affected SRX devices. Immediate patching and configuration review are recommended to mitigate impact.

Impact

For European organizations, this vulnerability poses a significant risk to network availability and operational continuity, especially for those relying on Juniper SRX Series devices for perimeter security, VPN termination, and traffic routing. A successful exploit can cause the packet forwarding engine to crash and restart, leading to temporary traffic loss and potential service outages. This can disrupt business-critical communications, impact remote access via IPsec VPNs, and degrade network performance. Sectors such as finance, telecommunications, government, and critical infrastructure operators in Europe that deploy Juniper SRX devices are particularly vulnerable. The unauthenticated, network-based nature of the attack vector means attackers can exploit this remotely without prior access, increasing the threat surface. Additionally, the default enabling of PMI means many devices may be exposed even without explicit configuration changes. The resulting denial of service could facilitate further attacks by distracting or disabling network defenses.

CWE-755Improper Handling of Exceptional Conditions (opens in a new tab)
Class weaknessLikelihood of exploit: MediumOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product does not handle or incorrectly handles an exceptional condition.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 22 Jan 2026, 21:26 UTC

WeaknessesCWE-755

Technical details

References

Community reviews

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