Medium [CVE-2026-0203] Improper Handling of Exceptional Conditions vulnerability in packet processing of Juniper Networks Junos OS
This medium-severity Juniper Networks advisory covers CVE-2026-0203 affecting Junos, Junos OS, MX.
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Summary
An Improper Handling of Exceptional Conditions vulnerability in packet processing of Juniper Networks Junos OS allows an unauthenticated, network-adjacent attacker sending a specifically malformed ICMP packet to cause an FPC to crash and restart, resulting in a Denial of Service (DoS).
When an ICMP packet is received with a specifically malformed IP header value, the FPC receiving the packet crashes and restarts. Due to the specific type of malformed packet, adjacent upstream routers would not forward the packet, limiting the attack surface to adjacent networks.
This issue only affects ICMPv4. ICMPv6 is not vulnerable to this issue.
This issue does not affect AFT-based line cards such as the MPC10, MPC11, LC4800, LC9600, and MX304.
This issue affects Junos OS:
- all versions before 21.2R3-S9,
- from 21.4 before 21.4R3-S10,
- from 22.3 before 22.3R3-S4,
- from 23.2 before 23.2R2-S3,
- from 23.4 before 23.4R2-S3,
Affected products named by the advisory: MX; EX.
- 21.4
- 22.2
- 22.3
- 22.4
- 23.2
- 23.4
- 24.2
- all versions
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 21.2R3-S9
- 21.4R3-S10
- 22.2R3-S7
- 22.3R3-S4
- 22.4R3-S5
- 23.2R2-S3
- 23.4R2-S3
- 24.2R1-S2
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation
Upgrade to a fixed release: 21.2R3-S9, 21.4R3-S10, 22.2R3-S7, 22.3R3-S4, 22.4R3-S5, 23.2R2-S3. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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