Bug 2553035 (CVE-2026-110926) - CVE-2026-110926 openssh: openssh: shared LZ77 compression dictionary leaks plaintext across channels
Summary: CVE-2026-110926 openssh: openssh: shared LZ77 compression dictionary leaks pl...
Keywords:
Status: NEW
Alias: CVE-2026-110926
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-10-15 04:20 UTC by OSIDB Bzimport
Modified: 2026-10-15 04:55 UTC (History)
18 users (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed:
Embargoed:

Attachments (Terms of Use)

Description OSIDB Bzimport 2026-10-15 04:20:17 UTC 
A flaw was found in OpenSSH. Outbound compression used deflateInit with the default level, so every channel on a connection shared one LZ77 search buffer. A peer who can write on one channel can recover plaintext from another channel by observing ciphertext lengths, as described in "Crossing the Streams" (Fabian Bäumer and Marcus Brinkmann, 2026). The fix switches outbound compression to Z_HUFFMAN_ONLY, which removes LZ77 matching and lowers the compression ratio. The RHEL maintainer will take that fix. The OpenSSH client does not offer compression by default. The server zlib default is delayed compression, which applies only if the client offers it.
Note You need to log in before you can comment on or make changes to this bug.