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:X/RE:M/U:XSummary
CVE-2026-21918 is a high-severity Double Free (CWE-415) vulnerability in Juniper Junos. Its CVSS base score is 8.7 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); 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 SA-8 (Security and Privacy Engineering Principles) — 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-2026-21918 is a Double Free vulnerability (CWE-415) in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series platforms. The issue occurs when a specific sequence of packets is encountered during TCP session establishment, triggering a double free that causes flowd to crash and the respective Flexible PIC Concentrator (FPC) to restart. This affects all versions of Junos OS prior to 22.4R3-S7, 23.2 versions before 23.2R2-S3, 23.4 versions before 23.4R2-S4, and 24.2 versions before 24.2R2. The vulnerability 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).
An unauthenticated, network-based attacker can exploit this vulnerability by sending the specific sequence of packets during TCP session establishment to any affected SRX or MX Series device. Successful exploitation results in a Denial-of-Service (DoS) condition, as the flowd crash and FPC restart disrupt traffic processing on the targeted platform.
Juniper's security advisory JSA106018, available at kb.juniper.net/JSA106018 and supportportal.juniper.net/JSA106018, details the affected versions and recommends upgrading to a patched release such as Junos OS 22.4R3-S7 or later, 23.2R2-S3 or later, 23.4R2-S4 or later, or 24.2R2 or later to mitigate the issue.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2697
Vulnerability Data
A Double Free vulnerability in the flow processing daemon (flowd) of Juniper Networks Junos OS on SRX and MX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). On all SRX and MX Series platforms, when during TCP…
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session establishment a specific sequence of packets is encountered a double free happens. This causes flowd to crash and the respective FPC to restart. This issue affects Junos OS on SRX and MX Series: * all versions before 22.4R3-S7, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2-S4, * 24.2 versions before 24.2R2.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 1 hardening rule · 1 OS baseline
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Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation explicitly includes dynamic analysis and fuzzing that locate double-free defects before release.
Security engineering principles can require memory-safe allocation patterns or language features that structurally eliminate double-free opportunities.
Flaw remediation processes require identification and correction of memory-management defects such as double free once discovered.
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.
Secure SDLC practices directly prevent double-free errors via static analysis, safe memory APIs, and testing.
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 in development can detect double-free conditions before release.
Secure development life cycle includes memory-safety practices that can prevent double-free bugs.
Application security requirements can mandate memory-safety rules that reduce double-free risk.
Secure system architecture and engineering principles can prescribe safe memory-management patterns.
Secure coding standards directly address proper use of free() and similar functions.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (1 rule)
- V-248590 OL 8 must clear the page allocator to prevent use-after-free attacks. prevents CWE-415