CVE-2021-0264Junos OS and Junos OS Evolved: MX Series with MPC10/MPC11, PTX10003, PTX10008: Line card may crash and restart when traffic is hitting a firewall filter having a term with syslog action configured
- 5.9MediumCVSS base score
- 1.0%Exploitation in 30 daysEPSS · top 36% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
A vulnerability in the processing of traffic matching a firewall filter containing a syslog action in Juniper Networks Junos OS on MX Series with MPC10/MPC11 cards installed, PTX10003 and PTX10008 Series devices, will cause the line card to crash and restart, creating a Denial of Service (DoS). Continued receipt and processing of packets matching the firewall filter can create a sustained Denial of Service (DoS) condition. When traffic hits the firewall filter, configured on lo0 or any physical interface on the line card, containing a term with a syslog action (e.g. 'term <name> then syslog'), the affected line card will crash and restart, impacting traffic processing through the ports of the line card. This issue only affects MX Series routers with MPC10 or MPC11 line cards, and PTX10003 or PTX10008 Series packet transport routers. No other platforms or models of line cards are affected by this issue. Note: This issue has also been identified and described in technical service bulletin TSB17931 (login required). This issue affects: Juniper Networks Junos OS on MX Series: 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R3-S2; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R2-S2, 20.2R3; 20.3 versions prior to 20.3R3; 20.4 versions prior to 20.4R2. Juniper Networks Junos OS Evolved on PTX10003, PTX10008: All versions prior to 20.4R2-EVO. This issue does not affect Juniper Networks Junos OS versions prior to 19.3R1.
Timeline
ID reserved
By juniper
- 6 months later
· 6 months later
Published
- 3 years later
· 3 years later
Record updated
- 2 years later
· 2 years later
EPSS rose above 1%
0.98% → 1.0%
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| juniperCNA (assigner) | 3.1 | Medium5.9 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Modified | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 1.0% · top 36% of all CVEs (12 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.9.
Affected products
- unaffected unspecified – < 19.3R1
- affected 19.3 – < 19.3R3-S2
- affected 19.4 – < 19.4R3-S2
- affected 20.1 – < 20.1R3
- affected 20.2 – < 20.2R2-S2, 20.2R3
- affected 20.3 – < 20.3R3
- affected 20.4 – < 20.4R2
Juniper Networks · Junos OS Evolved
- affected unspecified – < 20.4R2-EVO
What to do
Solution: The following software releases have been updated to resolve this specific issue: Junos OS 19.4R3-S2, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R3, 20.4R2, 21.1R1, and all subsequent releases. Junos OS Evolved 20.4R2-EVO, 21.1R1-EVO, and all subsequent releases.
Workaround: Remove the "syslog" action from the firewall filter configuration.
Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
References
References2
- https://kb.juniper.net/JSA11155 (opens in a new tab)x_refsource_MISCx_transferred
- https://kb.juniper.net/TSB17931 (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-2883 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-0264)Record last updated .