CVE-2026-39827: CVE-2026-39827: Denial of Service via Unbounded Memory Growth in Go SSH (golang.org/x/crypto/ssh)

#security #cve #cybersecurity

CVE-2026-39827: Denial of Service via Unbounded Memory Growth in Go SSH (golang.org/x/crypto/ssh)

Vulnerability ID: CVE-2026-39827
CVSS Score: 6.5
Published: 2026-06-25

An unbounded memory leak vulnerability in the Go SSH package (golang.org/x/crypto/ssh) allows authenticated users to crash the server by repeatedly requesting connection channels that are rejected, leading to system resource exhaustion.

TL;DR

A memory leak in golang.org/x/crypto/ssh prior to version 0.52.0 allows authenticated clients to trigger a Denial of Service by repeatedly sending channel requests that the server rejects.

Technical Details

CWE ID: CWE-401
Attack Vector: Network (AV:N)
CVSS Score: 6.5 (Medium)
EPSS Score: 0.00196
Impact: Denial of Service (DoS) / Memory Exhaustion
Exploit Status: None (No public exploits)
KEV Status: Not listed

Affected Systems

Go application servers using golang.org/x/crypto/ssh to run SSH server-side services
Gitea SSH servers
Docker/Podman daemon SSH components
HashiCorp Vault SSH secrets engine
golang.org/x/crypto/ssh: < 0.52.0 (Fixed in: 0.52.0)

Code Analysis

Commit: 6c195c8

ssh: remove rejected channels from connection's channel list

diff --git a/ssh/channel.go b/ssh/channel.go
index cc0bb7ab64..00e4cebb5d
--- a/ssh/channel.go
+++ b/ssh/channel.go
@@ -530,7 +530,17 @@ func (ch *channel) Reject(reason RejectionReason, message string) error {
        Language: "en",
    }
    ch.decided = true
-   return ch.sendMessage(reject)
+   err := ch.sendMessage(reject)
+
+   // Remove the channel from the mux to prevent memory leaks.
+   // Do not call ch.close() here: no goroutine holds a reference to a
+   // rejected channel's internal channels (msg, incomingRequests), so
+   // removing it from chanList is sufficient for GC. Calling close()
+   // would race with the mux loop goroutine (handlePacket or dropAll),
+   // causing a panic from closing an already-closed channel.
+   ch.mux.chanList.remove(ch.localId)
+
+   return err
 }

Mitigation Strategies

Upgrade golang.org/x/crypto to version 0.52.0 or higher.
Recompile all statically linked Go binaries using the updated library.
Implement monitoring for rapid SSH channel creation failures per session.

Remediation Steps:

Identify all internal Go projects that utilize the 'golang.org/x/crypto/ssh' package.
Run 'go get golang.org/x/crypto@v0.52.0' in the root directory of the affected projects.
Run 'go mod tidy' to update the dependency tree and lock files.
Rebuild the binaries and redeploy the affected applications.

References

Read the full report for CVE-2026-39827 on our website for more details including interactive diagrams and full exploit analysis.

DEV Community