CVE-2026-47736
ADVISORY - githubSummary
Impact
PROXY protocol support for Puma was added in version 5.5.0.
When PROXY protocol v1 support is enabled, Puma reads incoming bytes into an internal buffer. It waits for "\r\n" to determine whether a PROXY v1 line is present. If an attacker opens a TCP connection and continuously sends bytes without CRLF, Puma keeps appending to this pre-parse buffer.
This can cause unbounded in-process memory growth and additional CPU cost from repeatedly scanning the growing buffer for CRLF. A single, unauthenticated TCP connection can drive significant memory growth and may cause process/container OOM or degraded availability.
Only Puma servers using the following non-default config are affected:
set_remote_address proxy_protocol: :v1
Patches
Users should upgrade to versions 7.2.1 or 8.0.2.
Workarounds
- Disable PROXY protocol v1 parsing if it is not required:
# remove/comment this:
# set_remote_address proxy_protocol: :v1
- Restrict direct network access to Puma listeners using PROXY protocol:
- Only allow trusted load balancers/reverse proxies to connect.
- Block arbitrary client TCP access with firewall/security group rules.
Resources
Common Weakness Enumeration (CWE)
Uncontrolled Resource Consumption
GitHub
3.9
CVSS SCORE
7.5high| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| puma | gem | - | - | >=5.5.0,<7.2.1 | 7.2.1 |
| puma | gem | - | - | >=8.0.0,<8.0.2 | 8.0.2 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
There is no loss of trust or accuracy within the impacted component.
There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component.