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How CVE-2026-54909 Works
CVE-2026-54909 is a medium-severity vulnerability in the Pion STUN library, a widely-used Go implementation of the Session Traversal Utilities for NAT (STUN) protocol. The flaw resides in the `XORMappedAddress.GetFromAs` function, which is responsible for parsing the XOR-MAPPED-ADDRESS attribute from STUN messages.
STUN is a fundamental protocol for WebRTC and other real-time communication systems, used to discover public IP addresses and ports. During the ICE (Interactive Connectivity Establishment) process, clients and servers exchange STUN Binding requests and responses. The XOR-MAPPED-ADDRESS attribute in a response contains the client’s reflexive transport address, obfuscated via an XOR operation with a magic cookie.
The vulnerability arises because the `XORMappedAddress.GetFromAs` function fails to properly validate the length of incoming XOR-MAPPED-ADDRESS attributes before processing them. When it encounters a malformed attribute that is shorter than expected, the function attempts to read from an insufficient buffer. This out-of-bounds access triggers a runtime panic in Go.
A panic in Go causes the current goroutine to halt and unwinds its stack, typically crashing the entire application if the panic is not recovered. In the context of a STUN server or a WebRTC agent, this means a single malformed packet can bring down the entire service.
The attack vector is straightforward and dangerous: an unauthenticated attacker can send a specially crafted STUN or ICE Binding-response message containing a short XOR-MAPPED-ADDRESS attribute. This packet can be delivered over the network without any special privileges or user interaction. The attack complexity is low, making it trivial to execute. The impact is strictly a denial of service, affecting only the availability of the service, with no confidentiality or integrity compromise.
The issue has been assigned a CVSS v3.1 base score of 5.3 (Medium) by GitHub, Inc.. The vector string is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L, reflecting the network-based, low-complexity, unauthenticated nature of the attack.
The vulnerability affects all Pion STUN versions prior to v3.1.3. However, the official patch was released in v3.1.5, with the fix introduced via pull request 278. The commit fa9f074 contains the specific code changes that add proper length validation. No workarounds exist; upgrading is the only solution.
DailyCVE Form:
Platform: Pion STUN
Version: < 3.1.3
Vulnerability: Remote DoS via panic
Severity: Medium (CVSS 5.3)
date: July 31, 2026
Prediction: Patch expected August 2026
What Undercode Say
Analytics & Bash Commands
To check if your environment is vulnerable, you can inspect your `go.mod` file for the Pion STUN version:
grep "github.com/pion/stun" go.mod
To verify the version of an installed binary (if using Go modules):
go list -m github.com/pion/stun
For dependency scanning, use tools like `govulncheck`:
govulncheck ./...
To test for the vulnerability in a controlled environment, a malicious STUN packet with a short XOR-MAPPED-ADDRESS attribute can be crafted. A conceptual example using Python’s `scapy` (for illustration only) might look like:
from scapy.all import Craft a STUN Binding Response with a malformed XOR-MAPPED-ADDRESS (This is a simplified representation; actual implementation requires correct STUN headers and attributes) packet = IP(dst="target")/UDP(dport=3478)/Raw(load=b"\x01\x01\x00\x0c" + b"\x00"8 + b"\x00\x20\x00\x02" + b"\x01") send(packet)
How Exploit
An attacker can exploit this vulnerability by sending a single UDP packet to a vulnerable STUN server or a WebRTC agent that uses the Pion STUN library. The packet must be a STUN or ICE Binding-response message containing a malformed XOR-MAPPED-ADDRESS attribute that is shorter than the expected length. No authentication or special privileges are required. Upon receiving this packet, the `XORMappedAddress.GetFromAs` function panics, causing the application to crash and resulting in a denial of service. This attack can be performed remotely over the network.
Protection from this CVE
The only effective protection against CVE-2026-54909 is to upgrade the Pion STUN library to v3.1.5 or a later version. This version includes the patch from pull request 278, which fixes the improper input validation. There are no viable workarounds; the vendor explicitly states, “No work around; please upgrade to v3.1.5 or a newer version”. Administrators should prioritize this upgrade, especially for internet-facing deployments.
Impact
The impact of this vulnerability is a remote denial of service (DoS). An attacker can cause the affected application to panic and crash, making the service unavailable. The vulnerability is rated as Medium severity with a CVSS score of 5.3. The attack is unauthenticated, requires low complexity, and can be executed over the network. There is no impact on confidentiality or integrity. The vulnerability affects all versions prior to 3.1.3, but the patch is available in v3.1.5.
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Sources:
Reported By: github.com
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