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No exploitation reportedFix available

CVE-2026-62949

No exploitation reported by the sources we read.

  • Published2026-09-16
  • Fixed in2.24.0
  • WeaknessCWE-835

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.24.0, _process_channel_open and _process_channel_open_confirmation in asyncssh/connection.py accept a peer-supplied send_pktsize value of zero. When channel data reaches SSHChannel._flush_send_buf in asyncssh/channel.py, the zero value causes each loop iteration to slice and remove zero bytes without reducing the send window, leaving the synchronous loop permanently true with no await point. A malicious SSH server can trigger the client path through SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can trigger the server path through SSH_MSG_CHANNEL_OPEN and freeze every current and future connection handled by the process. This vulnerability is fixed in 2.24.0.

Timeline

dates in UTC
  1. 2026-09-1620:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-62949?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-62949?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV
asyncssh
BranchAffectedFixed in
2.24< 2.24.02.24.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-62949 Red Hat Product Security3 known affected

    asyncssh: AsyncSSH: Denial of Service via zero-sized SSH packets

    rhceph/rhceph-7-rhel9 as a component of Red Hat Ceph Storage 7 · rhceph/rhceph-8-rhel9 as a component of Red Hat Ceph Storage 8 · rhceph/rhceph-9-rhel9 as a component of Red Hat Ceph Storage 9

Full record on NVD

Fix

  1. Update asyncssh to 2.24.0
  2. Workaround from the vendor Red Hat Product Security CVE-2026-62949 · 3 productsUntil updates are available, administrators can implement the following mitigations to reduce the risk of event loop freeze attacks: 1. Restrict SSH connectivity for Ceph management and orchestration tools to trusted SSH servers only. Use firewall rules or network policies to prevent connections t…
  3. No fix available, says the vendor Red Hat Product Security CVE-2026-62949 · 3 productsFix deferred

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-09-17
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.16.5read 2026-10-23
  • CNAweakness (CWE)CWE-835read 2026-10-23
  • FIRST EPSSEPSS score0.4 %2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Published
2026-09-16
Last Modified
2026-09-30
NVD status
Awaiting Analysis

Frequently asked questions

What is CVE-2026-62949?

AsyncSSH is a Python package which provides an asynchronous client and server implementation of the SSHv2 protocol on top of the Python asyncio framework. Prior to 2.24.0, _process_channel_open and _process_channel_open_confirmation in asyncssh/connection.py accept a peer-supplied send_pktsize value of zero. When channel data reaches SSHChannel._flush_send_buf in asyncssh/channel.py, the zero value causes each loop iteration to slice and remove zero bytes without reducing the send window, leaving the synchronous loop permanently true with no await point. A malicious SSH server can trigger the client path through SSH_MSG_CHANNEL_OPEN_CONFIRMATION before the first channel write, while an authenticated client can trigger the server path through SSH_MSG_CHANNEL_OPEN and freeze every current and future connection handled by the process. This vulnerability is fixed in 2.24.0.

Is CVE-2026-62949 actively exploited?

Active exploitation of CVE-2026-62949 has not been confirmed. Its EPSS score was 0.4% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-62949?

CVE-2026-62949 has a CVSS v3 base score of 6.5 (MEDIUM severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

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