Bug 2383888 (CVE-2025-8277)

Summary: CVE-2025-8277 libssh: Memory Exhaustion via Repeated Key Exchange in libssh
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: adudiak, kshier, omaciel, security-response-team, stcannon, yguenane
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in libssh's handling of key exchange (KEX) processes when a client repeatedly sends incorrect KEX guesses. The library fails to free memory during these rekey operations, which can gradually exhaust system memory. This issue can lead to crashes on the client side, particularly when using libgcrypt, which impacts application stability and availability.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 2394049, 2394052, 2394044, 2394045, 2394046, 2394047, 2394048, 2394050, 2394051    
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Description OSIDB Bzimport 2025-07-28 11:06:00 UTC 
Memory Exhaustion vulnerability in the key exchange logic of the libssh library. When an authenticated client repeatedly performs rekeying with incorrect first_kex_packet_follows guesses, libssh allocates new ephemeral key pairs without freeing old ones stored in session->next_crypto. Over time, this results in a memory leak that can exhaust system memory and cause a client-side denial-of-service (DoS). This flaw affects several KEX algorithms (Curve25519, ECDH, sntrup761x25519, DH-GEX) across multiple crypto backends (libgcrypt, OpenSSL, mbedTLS). The issue requires an authenticated client and does not impact the server side.
Versions Affected : libssh >= 0.6.0
Comment 1 Abhishek Raj 2025-09-29 11:58:56 UTC 
Version affected : libssh >= 0.6.0, <= 0.11.3