CVE-2021-28511This advisory documents the impact of an internally found vulnerability in Arista EOS for security ACL bypass. The impact of this vulnerability is that the security ACL drop rule might be bypassed if a NAT ACL rule filter with permit action matches t ...
- 5.8MediumCVSS base score
- 0.60%Exploitation in 30 daysEPSS · top 51% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
This advisory documents the impact of an internally found vulnerability in Arista EOS for security ACL bypass. The impact of this vulnerability is that the security ACL drop rule might be bypassed if a NAT ACL rule filter with permit action matches the packet flow. This could allow a host with an IP address in a range that matches the range allowed by a NAT ACL and a range denied by a Security ACL to be forwarded incorrectly as it should have been denied by the Security ACL. This can enable an ACL bypass.
Timeline
ID reserved
By Arista
- 17 months later
· 17 months later
Published
- 4 years later
· 4 years later
Record updated
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 |
|---|---|---|---|
| AristaCNA (assigner) | 3.1 | Medium5.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N |
| NVDNVD · Modified | 3.1 | Medium6.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.60% · top 51% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.8.
Affected products
- affected 4.24.0 – ≤ 4.24.9
- affected 4.25.0 – ≤ 4.25.8
- affected 4.26.0 – ≤ 4.26.5
- affected 4.27.0 – ≤ 4.27.3
What to do
Solution: The recommended resolution is to upgrade to a remediated software version at your earliest convenience. The fixed versions for the currently supported release trains are as follows: 4.24.10 and later releases in the 4.24.x train 4.25.9 and later releases in the 4.25.x train 4.26.6 and later releases in the 4.26.x train 4.27.4 and later releases in the 4.27.x train 4.28.0 and later releases in the 4.28.x train
Workaround: Configure a NAT “drop” ACL rule for each security ACL “drop” rule that should be applied to the interface that has NAT configured. This will prevent the packets from being translated at the expense of maintaining the configuration in two places.
References
References1
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-2021-15187 (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-2021-28511)Record last updated .