CVE-2024-21661

An attacker can exploit a critical flaw in the application to initiate a Denial of Service (DoS) attack, rendering the application inoperable and affecting all users. The issue arises from unsafe manipulation of an array in a multi-threaded environment.

Details

The vulnerability is rooted in the application's code, where an array is being modified while it is being iterated over. This is a classic programming error but becomes critically unsafe when executed in a multi-threaded environment. When two threads interact with the same array simultaneously, the application crashes.

The core issue is located in expireOldFailedAttempts function:

func expireOldFailedAttempts(maxAge time.Duration, failures *map[string]LoginAttempts) int {

expiredCount := 0  
for key, attempt := range *failures {

if time.Since(attempt.LastFailed) > maxAge*time.Second { expiredCount += 1  
delete(*failures, key) // Vulnerable code

} }

return expiredCount }

The function modifies the array while iterating it which means the code will cause an error and crash the application pod, inspecting the logs just before the crash we can confirm:

goroutine 2032 [running]: github.com/argoproj/argo-cd/v2/util/session.expireOldFailedAttempts(0x12c, 0xc000adecd8)

/go/src/github.com/argoproj/argo-cd/util/session/sessionmanager.go:304 +0x7c github.com/argoproj/argo-cd/v2/util/session.(*SessionManager).updateFailureCount(0xc00035 af50, {0xc001b1f578, 0x11}, 0x1)

/go/src/github.com/argoproj/argo-cd/util/session/sessionmanager.go:320 +0x7f github.com/argoproj/argo-cd/v2/util/session.(*SessionManager).VerifyUsernamePassword(0xc 00035af50, {0xc001b1f578, 0x11}, {0xc000455148, 0x8})

PoC

To reproduce the vulnerability, you can use the following steps:

1. Launch the application.
2. Trigger the code path that results in the expireOldFailedAttempts() function being called in multiple threads.
3. In the attached PoC script we are restarting the server in a while loop, causing the application to be unresponsive at all.

This is a Denial of Service (DoS) vulnerability. Any attacker can crash the application continuously, making it impossible for legitimate users to access the service. The issue is exacerbated because it does not require authentication, widening the pool of potential attackers.

A write operation targets a memory location beyond the intended buffer boundary. Typical impact: memory corruption, crash, or arbitrary code execution.

CVE-2024-21661 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.8.13, 2.9.9, 2.10.4); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-21661? CVE-2024-21661 is a high-severity out-of-bounds write vulnerability in github.com/argoproj/argo-cd (go), affecting versions <= 1.8.7. It is fixed in 2.8.13, 2.9.9, 2.10.4. A write operation targets a memory location beyond the intended buffer boundary.
2. How severe is CVE-2024-21661? CVE-2024-21661 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2024-21661?
   • github.com/argoproj/argo-cd (go) (versions <= 1.8.7)
   • github.com/argoproj/argo-cd/v2 (go) (versions < 2.8.13)
4. Is there a fix for CVE-2024-21661? Yes. CVE-2024-21661 is fixed in 2.8.13, 2.9.9, 2.10.4. Upgrade to this version or later.
5. Is CVE-2024-21661 exploitable, and should I be worried? Whether CVE-2024-21661 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-21661 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-21661?
   • Upgrade github.com/argoproj/argo-cd/v2 to 2.8.13 or later
   • Upgrade github.com/argoproj/argo-cd/v2 to 2.9.9 or later
   • Upgrade github.com/argoproj/argo-cd/v2 to 2.10.4 or later