Description

In ssh in OpenSSH before 10.5, a use-after-free for realloc data can occur if a certain pair of remote-forwarding operations are concurrent.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "4.8",
  "pubDate": "2026-08-11T20:18:49.830Z",
  "pubdate": "2026-08-11T20:18:49.830Z",
  "executiveSummary": "A use-after-free vulnerability exists in the ssh component of OpenSSH before version 10.5, specifically involving memory management during the realloc data operation.\nThe flaw allows a remote threat actor to trigger memory corruption under specific concurrency conditions.\nThe vulnerability affects OpenSSH installations running versions prior to 10.5 where remote-forwarding operations are utilized.\nSuccessful exploitation of this memory safety issue compromises the integrity and availability of the affected ssh process, potentially leading to arbitrary code execution or denial of service depending on heap layout and allocator state.\nAttack capabilities require the ability to initiate and coordinate network-level interactions with the target ssh service.\nExploitation requirements dictate the precise execution of a specific pair of remote-forwarding operations in a concurrent manner to induce the race condition necessary for the use-after-free state.\nThe risk implication is critical for environments relying on secure shell infrastructure where concurrent forwarding requests can be manipulated, posing a threat to overall system confidentiality and stability.",
  "technicalDetails": "The vulnerability is rooted in memory management deficiencies within the ssh component of OpenSSH, specifically concerning the reallocation of data structures during remote-forwarding operations.\nThe vulnerable component handles memory buffers associated with remote forwarding requests, where improper reference tracking during buffer resizing operations leads to a use-after-free condition.\nThe affected versions comprise all OpenSSH releases prior to version 10.5.\nNetwork exposure is inherent to the ssh service, typically listening on TCP port 22 or configured alternative ports, where remote connections are accepted.\nAuthentication requirements and privilege requirements depend on the specific attack surface exposed by the forwarding mechanism, though the race condition relies on the processing of specific protocol messages.\nThe attack flow initiates when a malicious or compromised client executes a carefully timed sequence of operations.\nStep-by-step, exploitation occurs as follows: first, the attacker initiates a specific pair of remote-forwarding operations designed to target the memory allocation routines handling forwarding data.\nSecond, the attacker leverages network latency or concurrent connection threads to ensure these operations execute simultaneously or in rapid succession, creating a race condition.\nThird, during this race condition, one execution thread frees the memory buffer associated with the realloc data routine while another thread retains a dangling pointer to the same memory location.\nFourth, subsequent heap activity or manipulation by the attacker reallocates the freed memory region with controlled data, resulting in a use-after-free condition.\nPayload behavior following the successful triggering of the use-after-free can lead to unexpected application crashes causing a denial of service, or potentially facilitating arbitrary code execution if the application flow can be redirected through corrupted function pointers or data structures.\nPost-exploitation impact includes potential compromise of the ssh daemon process execution context, threatening connected sessions and underlying host security."
}