7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2025-22869

CVE-2025-22869: golang.org/x/crypto Vulnerable to Denial of Service (DoS) via Slow or Incomplete Key Exchange

SSH servers which implement file transfer protocols are vulnerable to a denial of service attack from clients which complete the key exchange slowly, or not at all, causing pending content to be read into memory, but never transmitted.

(GitHub Advisory)

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CVE-2025-22869

CVE-2025-22869:

7.5

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
golang.org/x/crypto	go	< 0.35.0	0.35.0

Technical Details

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Root Cause Analysis

The analysis focused on the provided commit 7292932d45d55c7199324ab0027cc86e8198aa22 for the golang/crypto repository. The commit message explicitly states: 'ssh: limit the size of the internal packet queue while waiting for KEX'. It describes that while a key exchange is in progress, packets were added to an internal queue (pendingPackets) without a limit. This could lead to high memory usage or exhaustion if the other party was slow or unresponsive during key exchange.

The diff for ssh/handshake.go shows changes primarily in the handshakeTransport struct and its methods. The key change is within the writePacket method.

Before the patch, the code was:

	if t.sentInitMsg != nil {
		// Copy the packet so the writer can reuse the buffer.
		cp := make([]byte, len(p))
		copy(cp, p)
		t.pendingPackets = append(t.pendingPackets, cp)
		return nil
	}

This section shows that if t.sentInitMsg is not nil (meaning a key exchange is in progress), the packet p is copied and appended to t.pendingPackets without any size check on t.pendingPackets.

The patch introduces a check for len(t.pendingPackets) < maxPendingPackets and a loop that waits on t.writeCond.Wait() if the queue is full, thus mitigating the unbounded growth of pendingPackets.

Therefore, the (*handshakeTransport).writePacket function is identified as the vulnerable function because it's where the unbounded queuing of packets occurred during a pending key exchange, leading to potential DoS.

Vulnerable functions

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Reasoning

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