Raw vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:C/RE:M/U:AmberSummary
CVE-2026-21905 is a high-severity Infinite Loop (CWE-835) vulnerability in Juniper Junos. Its CVSS base score is 8.7 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 30th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-21905 is a Loop with Unreachable Exit Condition (infinite loop) vulnerability, classified under CWE-835, in the Session Initiation Protocol (SIP) application layer gateway (ALG) of Juniper Networks Junos OS. It affects SRX Series devices and MX Series routers equipped with MX-SPC3 or MS-MPC service cards. The vulnerability arises when the SIP ALG incorrectly parses multiple SIP headers in messages received over TCP, leading to a continuous parsing loop that triggers a watchdog timer expiration. This crashes the flowd process on SRX Series and MX Series with MX-SPC3, or the mspmand process on MX Series with MS-MPC. The issue does not affect SIP messages over UDP and has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Vulnerable versions include all releases prior to 21.2R3-S10, and specific ranges in the 21.4, 22.4, 23.2, 23.4, 24.2, 24.4, and 25.2 series.
An unauthenticated, network-based attacker can exploit this vulnerability by sending crafted SIP messages over TCP to a vulnerable device. Receipt of multiple such messages triggers the infinite loop in the SIP ALG, causing the flow management process to crash and resulting in a Denial of Service (DoS) condition. The crash disrupts traffic processing on the affected service cards, potentially impacting SIP-related traffic forwarding until the process restarts.
Juniper Security Advisory JSA106004, available at kb.juniper.net/JSA106004 and supportportal.juniper.net/JSA106004, details the affected versions and recommends upgrading to a fixed release, such as 21.2R3-S10 or later non-vulnerable versions in the specified series, to mitigate the issue. No workarounds are mentioned in the provided information.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2687
Vulnerability Data
A Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in the SIP application layer gateway (ALG) of Juniper Networks Junos OS on SRX Series and MX Series with MX-SPC3 or MS-MPC allows an unauthenticated network-based attacker sending specific SIP messages…
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over TCP to crash the flow management process, leading to a Denial of Service (DoS). On SRX Series, and MX Series with MX-SPC3 or MS-MPC service cards, receipt of multiple SIP messages causes the SIP headers to be parsed incorrectly, eventually causing a continuous loop and leading to a watchdog timer expiration, crashing the flowd process on SRX Series and MX Series with MX-SPC3, or mspmand process on MX Series with MS-MPC. This issue only occurs over TCP. SIP messages sent over UDP cannot trigger this issue. This issue affects Junos OS on SRX Series and MX Series with MX-SPC3 and MS-MPC: * all versions before 21.2R3-S10, * from 21.4 before 21.4R3-S12, * from 22.4 before 22.4R3-S8, * from 23.2 before 23.2R2-S5, * from 23.4 before 23.4R2-S6, * from 24.2 before 24.2R2-S3, * from 24.4 before 24.4R2-S1, * from 25.2 before 25.2R1-S1, 25.2R2.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover unreachable loop exit conditions through static analysis, fuzzing, or execution tracing.
Flaw remediation processes identify and correct infinite-loop defects reported from testing or operations.
Requiring documented development processes and secure coding standards reduces introduction of loops whose termination conditions are unreachable.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can uncover infinite-loop conditions before release.
Secure development life cycle mandates practices that can detect and prevent infinite-loop defects.
Application security requirements can specify loop-termination rules, indirectly reducing the weakness.
Secure coding standards directly address loop termination and prevent infinite loops.
Secure architecture principles encourage designs that avoid unreachable exit conditions.
Change management can require review of loop logic when code is modified.