CVE-2021-29509
CVE-2021-29509 — Keepalive Connections Causing Denial Of Service in puma
Puma is a concurrent HTTP 1.1 server for Ruby/Rack applications. The fix for CVE-2019-16770 was incomplete. The original fix only protected existing connections that had already been accepted from having their requests starved by greedy persistent-connections saturating all threads in the same process. However, new connections may still be starved by greedy persistent-connections saturating all threads in all processes in the cluster. A `puma` server which received more concurrent `keep-alive` connections than the server had threads in its threadpool would service only a subset of connections, denying service to the unserved connections. This problem has been fixed in `puma` 4.3.8 and 5.3.1. Setting `queue_requests false` also fixes the issue. This is not advised when using `puma` without a reverse proxy, such as `nginx` or `apache`, because you will open yourself to slow client attacks…
Published Updated Sources: cvelistV5, GitHub_M
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.
Exploitation
Unreported
no source claims exploitation
EPSS
2%
chance of exploitation in 30 days
CVSS base
7.5
HIGH
Affected scope
The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.
Vendors (1)
Products (1)
Every base score collected
Sources score independently and disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Source |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | HIGH | — | — | cvelistV5 |
Weakness & attack patterns
- CWE-400
Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.
- T1499Endpoint Denial of Service
Detection
Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.
- Search application, proxy, and WAF logs for requests touching /Rack.
References
6 on the record
- github.com/puma/puma/security/advisories/GHSA-q28m-8xjw-8vr5
x_refsource_CONFIRM
- gist.github.com/nateberkopec/4b3ea5676c0d70cbb37c82d54be25837
x_refsource_MISC
- github.com/puma/puma/security/policy
x_refsource_MISC
- rubygems.org/gems/puma
x_refsource_MISC
- security.gentoo.org/glsa/202208-28
vendor-advisory, x_refsource_GENTOO
- lists.debian.org/debian-lts-announce/2022/08/msg00015.html
mailing-list, x_refsource_MLIST
Elsewhere on this site
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.