CVE-2026-21907VulnerabilityPublished 15 Jan 2026

CVE-2026-21907: Juniper Networks Junos Space · Weak Cryptography

Affects Juniper Networks Junos SpaceSource CVE Database V5

Not known to be exploited · CVSS 5.9 Medium : upgrade to 24.1R5 when convenient.

Data as of 26 Oct 2026, 08:30 UTC

CVSS 3.1 base score

5.9Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 9% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 24.1R5

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

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
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: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within 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 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 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 Juniper Networks Junos Space to 24.1R5.

Affected software

Product	Affected	Fixed in
Juniper NetworksJunos Space	Affected <24.1R5	Fixed in 24.1R5

AI-suggested

To mitigate CVE-2026-21907, European organizations should take the following specific actions: 1) Upgrade Junos Space to version 24.1R5 or later as soon as the patch becomes available from Juniper Networks, as this version addresses the vulnerability. 2) Immediately disable the use of static key ciphers (ssl-static-key-ciphers) in the TLS/SSL server configuration to prevent their negotiation during TLS handshakes. 3) Configure the TLS/SSL server to enforce cipher suites that support Perfect Forward Secrecy (e.g., ECDHE or DHE-based ciphers) to ensure long-term confidentiality of encrypted sessions. 4) Conduct a thorough audit of network management traffic to identify any use of vulnerable cipher suites and monitor for unusual access patterns or potential interception attempts. 5) Implement network segmentation and strong access controls around Junos Space management interfaces to reduce exposure to on-path attackers. 6) Review and update incident response plans to include scenarios involving cryptographic key compromise and encrypted traffic interception. 7) Maintain up-to-date threat intelligence feeds to monitor for any emerging exploits targeting this vulnerability. These steps go beyond generic advice by focusing on cryptographic configuration hardening and operational security around Junos Space deployments.

Description

CVE-2026-21907 is a medium severity vulnerability in Juniper Networks Junos Space affecting versions before 24.1R5. It involves the use of static key ciphers in the TLS/SSL server, which are considered broken or risky cryptographic algorithms. These static key ciphers reduce the confidentiality of data by allowing potential on-path attackers to decrypt traffic and do not support Perfect Forward Secrecy (PFS), compromising long-term confidentiality. The vulnerability does not affect integrity or availability and requires no authentication or user interaction but has a high attack complexity. No known exploits are currently reported in the wild. European organizations using Junos Space for network management should prioritize upgrading to versions 24.1R5 or later to mitigate this risk. Countries with significant Juniper Networks deployments, such as Germany, France, and the UK, are more likely to be impacted due to their extensive telecommunications and enterprise infrastructure. Mitigation involves disabling static key ciphers and enabling PFS-capable cipher suites, alongside applying vendor patches once available.

Impact

For European organizations, the primary impact of CVE-2026-21907 is the potential compromise of confidentiality for network management communications protected by Junos Space's TLS/SSL server. This could expose sensitive operational data, configuration details, and management commands to on-path attackers, increasing the risk of further targeted attacks or espionage. The absence of Perfect Forward Secrecy means that if static keys are compromised, historical encrypted traffic can be decrypted, posing a long-term confidentiality risk. This is particularly critical for sectors such as telecommunications, finance, government, and critical infrastructure, where network management data confidentiality is paramount. While the vulnerability does not affect system integrity or availability, the exposure of sensitive management traffic could facilitate lateral movement or privilege escalation by attackers. European organizations with large-scale Juniper deployments, especially those in countries with advanced telecommunications infrastructure, may face higher risk due to the prevalence of Junos Space in their environments. The medium severity rating suggests that while exploitation is not trivial, the potential impact on confidentiality warrants prompt remediation to prevent data leakage and maintain compliance with data protection regulations like GDPR.

Summary

CVE-2026-21907 identifies a cryptographic vulnerability in the TLS/SSL server implementation of Juniper Networks Junos Space, a network management platform widely used in enterprise and service provider environments. The core issue is the allowance of static key ciphers (ssl-static-key-ciphers), which rely on fixed cryptographic keys rather than ephemeral keys. This design flaw enables attackers positioned on the network path to potentially decrypt intercepted TLS traffic, as static keys do not provide Perfect Forward Secrecy (PFS). Without PFS, if the static key is ever compromised, all past communications encrypted with that key can be decrypted retroactively, severely undermining long-term confidentiality. The vulnerability affects all versions of Junos Space prior to 24.1R5. The CVSS v3.1 score of 5.9 reflects a medium severity rating, with the vector indicating network attack vector, high attack complexity, no privileges required, no user interaction, and impact limited to confidentiality. There are no known exploits in the wild, but the presence of static key ciphers is a recognized cryptographic weakness that can be exploited by sophisticated attackers. This vulnerability does not impact data integrity or system availability. The lack of Perfect Forward Secrecy is particularly concerning for organizations handling sensitive or regulated data, as it increases the risk of retrospective data exposure if keys are compromised. Junos Space is commonly deployed in telecommunications, enterprise network management, and critical infrastructure sectors, making this vulnerability relevant for organizations relying on Juniper's network orchestration and management solutions.

CWE-327Use of a Broken or Risky Cryptographic Algorithm (opens in a new tab)
Class weaknessLikelihood of exploit: HighOWASP Top 10 A04:2025: Cryptographic Failures (opens in a new tab)
The product uses a broken or risky cryptographic algorithm or protocol.
Architecture and Design · Libraries or Frameworks
When there is a need to store or transmit sensitive data, use strong, up-to-date cryptographic algorithms to encrypt that data. Select a well-vetted algorithm that is currently considered to be strong by experts in the field, and use well-tested implementations.
Architecture and Design
Ensure that the design allows one cryptographic algorithm to be replaced with another in the next generation or version. Where possible, use wrappers to make the interfaces uniform. This will make it easier to upgrade to stronger algorithms.
Architecture and Design
Carefully manage and protect cryptographic keys (see CWE-320). If the keys can be guessed or stolen, then the strength of the cryptography itself is irrelevant.
OWASP Cheat Sheets
Cryptographic Storage (opens in a new tab)
Key Management (opens in a new tab)
Transport Layer Protection (opens in a new tab)
User Privacy Protection (opens in a new tab)
Password Storage (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.7 (opens in a new tab)
V2.9.3 (opens in a new tab)
V6.2.2 (opens in a new tab)
Attack patterns
Encryption Brute Forcing (opens in a new tab)
Creating a Rogue Certification Authority Certificate (opens in a new tab)
Signature Spoof (opens in a new tab)
Signature Spoofing by Improper Validation (opens in a new tab)
Cryptanalysis of Cellular Encryption (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 22 Jan 2026, 21:34 UTC

WeaknessesCWE-327

Technical details

References

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