CVE-2021-0247
Published: 22 April 2021
Summary
CVE-2021-0247 is a medium-severity Race Condition (CWE-362) vulnerability in Juniper Junos. Its CVSS base score is 5.1 (Medium).
Operationally, ranked at the 46.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2021-2866
Vulnerability details
A Race Condition (Concurrent Execution using Shared Resource with Improper Synchronization) vulnerability in the firewall process (dfwd) of Juniper Networks Junos OS allows an attacker to bypass the firewall rule sets applied to the input loopback filter on any interfaces…
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of a device. This issue is detectable by reviewing the PFE firewall rules, as well as the firewall counters and seeing if they are incrementing or not. For example: show firewall Filter: __default_bpdu_filter__ Filter: FILTER-INET-01 Counters: Name Bytes Packets output-match-inet 0 0 <<<<<< missing firewall packet count This issue affects: Juniper Networks Junos OS 14.1X53 versions prior to 14.1X53-D53 on QFX Series; 14.1 versions 14.1R1 and later versions prior to 15.1 versions prior to 15.1R7-S6 on QFX Series, PTX Series; 15.1X53 versions prior to 15.1X53-D593 on QFX Series; 16.1 versions prior to 16.1R7-S7 on QFX Series, PTX Series; 16.2 versions prior to 16.2R2-S11, 16.2R3 on QFX Series, PTX Series; 17.1 versions prior to 17.1R2-S11, 17.1R3-S2 on QFX Series, PTX Series; 17.2 versions prior to 17.2R1-S9, 17.2R3-S3 on QFX Series, PTX Series; 17.3 versions prior to 17.3R2-S5, 17.3R3-S7 on QFX Series, PTX Series; 17.4 versions prior to 17.4R2-S9, 17.4R3 on QFX Series, PTX Series; 18.1 versions prior to 18.1R3-S9 on QFX Series, PTX Series; 18.2 versions prior to 18.2R2-S6, 18.2R3-S3 on QFX Series, PTX Series; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3-S1 on QFX Series, PTX Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R2-S7, 18.4R3 on QFX Series, PTX Series; 19.1 versions prior to 19.1R1-S4, 19.1R2-S1, 19.1R3 on QFX Series, PTX Series; 19.2 versions prior to 19.2R1-S3, 19.2R2 on QFX Series, PTX Series.
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Accurate timestamps from internal clocks enable detection of race conditions by providing reliable event ordering in audit logs.
Coordination of concurrent security activities reduces the probability that shared resources will be accessed simultaneously without proper synchronization.