libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
CVE-2026-55199
“—” beside the score: it is equal to NVD's CVSS score.
This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.9% (60th percentile of EPSS-scored CVEs). GitHub Security Advisory CVSS 5.9 is lower than this score; a lower GitHub score revises it only when its advisory is newer than the CVE record's last change, and this advisory (published 2026-06-17) is not newer than that change (2026-07-14), so it does not.
Also known asEUVD-2026-37782 (ENISA EUVD) · GHSA-3cfq-4xx4-rmpg (GitHub Security Advisories)Source: ENISA EUVD
- High severity, but no confirmed exploitation yet
A fix is available — apply it.
- CVSS v3
- 7.5
- EG Score
- 7.5HIGHmedium confidence
- EG Risk
- 34EG Risk 34/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity75% × 45%Impact severity (EG Severity): CVSS 7.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation0.9% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines. - EPSS PROB
- 0.9%
- EPSS %ILE
- 60th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.5): severity, escalated by confirmed exploitation. This CVE's 7.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
- EG Likelihood
- 0.9% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-31). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
June 17, 2026
Last Modified
July 14, 2026
Advisory Details (3)
Auto-updated Jun 17, 2026libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler | Advisories | VulnCheck
https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handlerpacket.c: check _libssh2_get_string() return in EXT_INFO handler
Upstream fix in progress (PR #1864 · libssh2/libssh2, state=closed)
https://github.com/libssh2/libssh2/pull/1864commit 17626857d20b (libssh2/libssh2)
Fix landed in libssh2/libssh2 commit 17626857d20b — awaiting tagged release
https://github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4Vendor Advisories for CVE-2026-55199(3)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- CVE-2026-55199Microsoft Security Response Center (MSRC)High
libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler
- RHSA-2026:29950Red Hat Product SecurityMedium
Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update
- GHSA-3cfq-4xx4-rmpgGitHub Security AdvisoriesHigh
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service...
Patch Availability(2)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| ubuntu | libssh2-1t64 (1.11.1-1ubuntu0.26.04.2) @ resolute | 2026-10-24 | ubuntu |
| redhat | libssh2-main-1.11.1-8.hum1 | 2026-06-25 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(7 across 6 ecosystems)
Alpine:v3.24(2)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | — |
| — |
| rust | — |
| — |
Alpine:v3.21(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | — |
| — |
Alpine:v3.22(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | — |
| — |
Alpine:v3.23(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | — |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | 1.11.1-1 |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| libssh2 | 1.11.1-1, 1.11.1-2, 1.11.1-3 |
| — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Additional Vendor Advisories
(1)
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Data Freshness Timeline
(refreshed 10× in last 7d / 45× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 100 of 347 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 247 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-02 16:45 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-11-01 00:41 UTCEG score recompute
- 2026-11-01 00:41 UTCVendor advisory
- 2026-11-01 00:41 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.9% · 60th percentile
- 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-25 14:19 UTCEG score recompute
- 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-24 14:04 UTCEG score recompute
- 2026-10-24 14:04 UTCVendor advisory
- 2026-10-24 14:04 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-18 03:30 UTCEG score recompute
- 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.9% · 59th percentile
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- 2026-10-17 03:26 UTCEG score recompute
- 2026-10-17 03:26 UTCVendor advisory
- 2026-10-17 03:26 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-10-16 16:42 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-12 15:56 UTCEG score recompute
- 2026-10-11 19:39 UTCEG score recompute
- 2026-10-11 16:54 UTCEG score recompute
- 2026-10-11 14:17 UTCEG score recompute
- 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.9% · 59th percentile
- 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-03 06:09 UTCOSV refresh
- 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.7% · 51st percentile
- 2026-09-29 15:22 UTCEPSS rescoreEPSS 0.7% · 50th percentile
- 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.7% · 50th percentile
- 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.7% · 50th percentile
- 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.7% · 50th percentile
- 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.7% · 50th percentile
- 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-14 03:05 UTCEG score recompute
- 2026-09-14 03:05 UTCVendor advisory
- 2026-09-14 03:05 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-13 14:07 UTCEG score recompute
- 2026-09-13 14:07 UTCVendor advisory
- 2026-09-13 14:07 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.9% · 58th percentile
- 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-30 21:16 UTCEG score recompute
- 2026-08-30 21:16 UTCVendor advisory
- 2026-08-30 21:16 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-24 22:22 UTCEG score recompute
- 2026-08-24 22:22 UTCVendor advisory
- 2026-08-24 22:22 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-08-24 05:18 UTCVendor advisory
- 2026-08-24 05:18 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-08-23 16:30 UTCVendor advisory
- 2026-08-23 16:30 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-08-23 03:53 UTCEG score recompute
- 2026-08-23 03:53 UTCVendor advisory
- 2026-08-23 03:53 UTCGHSA enrichmentGHSA-3cfq-4xx4-rmpg · GitHub severity HIGH · GitHub CVSS 5.9
- 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.9% · 57th percentile
- 2026-08-21 22:30 UTCVendor advisory
Related CVEs(same product + same vendor + same CWE)
Same product
10 shownAlpine:v3.24:rust · Alpine:v3.21:libssh2
- CVE-2026-55200EG 8.3EPSS p90HIGH
- CVE-2019-3861EG 9.1EPSS p92CRITICAL
- CVE-2019-3860EG 9.1EPSS p93CRITICAL
- CVE-2019-3858EG 9.1EPSS p94CRITICAL
- CVE-2019-3862EG 9.1EPSS p95CRITICAL
- CVE-2019-3859EG 9.1EPSS p94CRITICAL
- CVE-2023-48795NVD 5.9EG 9.0EPSS p100CRITICAL
- CVE-2019-3857EG 8.8EPSS p93HIGH
- CVE-2019-3856EG 8.8EPSS p93HIGH
- CVE-2019-3863EG 8.8HIGH
Same vendor
2 shownredhat:RHSA-2026:29950 · ubuntu:USN-8486-1
Frequently asked(5)
What is CVE-2026-55199?
When was CVE-2026-55199 made public?
Is CVE-2026-55199 actively exploited?
What is the CVSS score of CVE-2026-55199?
How do I remediate CVE-2026-55199?
Dependency Blast Radius
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