OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address space. One third-party report states "remote code execution is theoretically possible."
CVE-2023-25136
“▲” beside the score: it is higher than NVD's CVSS score.
Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2023-02-03. NVD baseline CVSS 6.5; sources differ by 3.3.
- 3 internet-facing services (distinct ip:port) on record running an affected version — derived from Shodan data (© Shodan); a patched service can stay counted while its port stays open
- High exploitation likelihood — EPSS 90%
- Public exploit or proof-of-concept code is available
A fix is available — apply it.
3 internet-facing services (distinct ip:port) on record running a version that maps to CVE-2023-25136, in our KEV-Exposure radar’s Shodan-derived sample.
How it counts: every 12 hours, when Shodan query credits allow, the radar runs one Shodan query per tracked product, reads up to 100 ip:port services per query, and keeps a service when its banner version matches a CISA-KEV or high-EPSS CVE; a service is dropped when neither a search nor a Shodan InternetDB port re-check has refreshed it for 21 days. A re-check that finds the port still listed by Shodan InternetDB refreshes the service without re-reading the banner, so a patched service can stay counted while its port stays open. A count is a banner-version inference over a sample, not an exploit test and not an internet-wide census, and the unit is a service, not a machine: a machine answering on two ports counts twice.
- CVSS v3
- 6.5
- EG Score
- 9.8CRITICALmedium confidence
- EG Risk
- 80EG Risk 80/100
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)Severity98% × 45%Impact severity (EG Severity): CVSS 9.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation90% × 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 low or medium mission impact; Track* at high (mission-essential systems).Exploitation public PoC (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
- 90%
- EPSS %ILE
- 99th
- 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 (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 90% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-22). 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 low or medium mission impact; Track* at high (mission-essential systems).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: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation public PoC (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.
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
February 3, 2023
Last Modified
October 14, 2026
Advisory Details (10)
Auto-updated Oct 14, 2026oss-security - Re: Re: double-free vulnerability in OpenSSH server 9.1 (CVE-2023-25136)
http://www.openwall.com/lists/oss-security/2023/02/23/3oss-security - Re: Re: double-free vulnerability in OpenSSH server 9.1 (CVE-2023-25136)
http://www.openwall.com/lists/oss-security/2023/02/22/2oss-security - Re: double-free vulnerability in OpenSSH server 9.1 (CVE-2023-25136)
http://www.openwall.com/lists/oss-security/2023/02/22/1oss-security - Re: double-free vulnerability in OpenSSH server 9.1 (CVE-2023-25136)
http://www.openwall.com/lists/oss-security/2023/02/13/1OpenSSH Pre-Auth Double Free – Writeup and Proof-of-Concept | Hacker News
https://news.ycombinator.com/item?id=34711565CVE-2023-25136 OpenSSH Pre-Auth Double Free Writeup & PoC
https://jfrog.com/blog/openssh-pre-auth-double-free-cve-2023-25136-writeup-and-proof-of-concept/commit 486c4dc3b83b (openssh/openssh-portable)
Fix landed in openssh/openssh-portable commit 486c4dc3b83b — awaiting tagged release
https://github.com/openssh/openssh-portable/commit/486c4dc3b83b4b67d663fb0fa62bc24138ec3946oss-security - double-free vulnerability in OpenSSH server 9.1
https://www.openwall.com/lists/oss-security/2023/02/02/2Vendor Advisories for CVE-2023-25136(2)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- CVE-2023-25136Microsoft Security Response Center (MSRC)Medium
OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms handling. This is fixed in OpenSSH 9.2. The double free can be leveraged, by an unauthenticated remote attacker in the default configuration, to jump to any location in the sshd address space. One third-party report states "remote code execution is theoretically possible."
- GHSA-w62j-g234-3f6fGitHub Security AdvisoriesCritical
OpenSSH server (sshd) 9.1 introduced a double-free vulnerability during options.kex_algorithms...
Patch Availability(1)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| redhat | openssh-0:8.7p1-29.el9_2 | 2023-05-09 | 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
(3 across 3 ecosystems)
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| openssh | — |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| openssh | — |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| openssh | — |
| — |
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 22× in last 7d / 46× 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 92 of 105 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. 8 repeat rows among the latest 100 are merged into the row they repeat. The 13 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-10-23 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-23 15:06 UTCEG score recompute
- 2026-10-23 15:06 UTCVendor advisory
- 2026-10-23 15:06 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-22 13:26 UTCEG score recompute
- 2026-10-22 13:26 UTCVendor advisory
- 2026-10-22 13:25 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-21 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-21 11:43 UTCEG score recompute
- 2026-10-21 11:43 UTCVendor advisory
- 2026-10-21 11:43 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-20 10:02 UTCEG score recompute
- 2026-10-20 10:02 UTCVendor advisory
- 2026-10-20 10:02 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-19 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-19 08:19 UTCEG score recompute
- 2026-10-19 08:19 UTCVendor advisory
- 2026-10-19 08:19 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-18 06:38 UTCEG score recompute
- 2026-10-18 06:38 UTCVendor advisory
- 2026-10-18 06:38 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-17 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-17 04:57 UTCEG score recompute
- 2026-10-17 04:57 UTCVendor advisory
- 2026-10-17 04:57 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
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- 2026-10-16 03:16 UTCEG score recompute
- 2026-10-16 03:16 UTCVendor advisory
- 2026-10-16 03:16 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-15 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-14 23:27 UTCVendor advisory
- 2026-10-14 23:27 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-14 22:34 UTCEG score recompute
- 2026-10-14 22:34 UTCVendor advisory
- 2026-10-14 22:34 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-14 16:29 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-13 20:13 UTCEG score recompute
- 2026-10-13 20:13 UTCVendor advisory
- 2026-10-13 20:12 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-12 17:31 UTCEG score recompute
- 2026-10-12 17:31 UTCVendor advisory
- 2026-10-12 17:31 UTCGHSA enrichmentGHSA-w62j-g234-3f6f · GitHub severity CRITICAL · GitHub CVSS 9.8
- 2026-10-11 21:57 UTCEG score recompute
- 2026-10-08 17:05 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-10-05 17:40 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-30 16:18 UTCEG score recompute
- 2026-09-24 14:01 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-23 21:41 UTCOSV refresh
- 2026-09-22 14:45 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-18 19:25 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-16 14:05 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-12 14:58 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-08 21:57 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-06 13:45 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-05 15:25 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-09-04 16:24 UTCOSV refresh
- 2026-08-30 19:15 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-28 21:38 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-25 13:46 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-24 14:14 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-19 17:01 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-18 03:34 UTCOSV refresh
- 2026-08-16 14:53 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-16 02:12 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-12 13:48 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-08 16:34 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-06 13:44 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-08-02 22:27 UTCOSV refresh
- 2026-08-01 04:13 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-28 15:34 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-25 14:16 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-24 14:15 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-23 02:19 UTCEG score recompute
- 2026-07-22 23:07 UTCEG score recompute
- 2026-07-22 14:06 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-16 07:19 UTCOSV refresh
- 2026-07-15 16:56 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-13 22:28 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-11 08:25 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-07-02 16:58 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-06-28 06:22 UTCOSV refresh
- 2026-06-27 03:07 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-06-24 14:03 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-06-23 21:31 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-06-15 17:47 UTCEPSS rescoreEPSS 90% · 99th percentile
- 2026-06-14 23:16 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-12 23:10 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-10 22:17 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-10 17:17 UTCOSV refresh
- 2026-06-10 13:21 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-08 14:15 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-07 15:23 UTCEPSS rescoreEPSS 88% · 99th percentile
- 2026-06-05 22:46 UTCEPSS rescoreEPSS 88% · 99th percentile
Publicly available exploits
(8 references)Public exploit code is referenced for this CVE (8 GitHub PoCs). Defenders should treat patch urgency accordingly.
- GitHub PoCmalvika-thakur/CVE-2023-25136Published Sep 21, 2023
OpenSSH Pre-Auth Double Free CVE-2023-25136 – Writeup and Proof-of-Concept
Open source ↗ - GitHub PoCH4K6/CVE-2023-25136Published Jun 30, 2023
OpenSSH 9.1漏洞大规模扫描和利用
Open source ↗ - GitHub PoCaxylisdead/CVE-2023-25136_POCPublished Jun 3, 2023
CVE-2023-25136 POC written by axylisdead
Open source ↗ - GitHub PoCnhakobyan685/CVE-2023-25136Published Apr 28, 2023
OpenSSH 9.1 vulnerability mass scan and exploit
Open source ↗ - GitHub PoCadhikara13/CVE-2023-25136Published Apr 18, 2023
OpenSSH Pre-Auth Double Free CVE-2023-25136 POC
Open source ↗ - GitHub PoCChristbowel/CVE-2023-25136Published Feb 22, 2023
OpenSSH 9.1 vulnerability mass scan and exploit
Open source ↗ - Open source ↗GitHub PoCticofookfook/CVE-2023-25136Published Feb 14, 2023
- Open source ↗GitHub PoCjfrog/jfrog-CVE-2023-25136-OpenSSH_Double-FreePublished Feb 7, 2023
Related CVEs(same product + same CWE)
Same product
10 shownDebian:12:openssh
- CVE-2003-0786EG 10.0HIGH
- CVE-2003-0693EG 10.0EPSS p96HIGH
- CVE-2002-0640EG 10.0EPSS p98HIGH
- CVE-2023-51385NVD 6.5EG 9.8EPSS p97CRITICAL
- CVE-2023-38408EG 9.8EPSS p100CRITICAL
- CVE-2023-28531EG 9.8CRITICAL
- CVE-2016-1908EG 9.8EPSS p97CRITICAL
- CVE-2002-0639EG 9.8EPSS p97CRITICAL
- CVE-2026-60002EG 9.4CRITICAL
- CVE-2024-6387NVD 8.1EG 9.0EPSS p100CRITICAL
Frequently asked(5)
What is CVE-2023-25136?
When was the CVE record for CVE-2023-25136 published?
Is CVE-2023-25136 actively exploited?
What is the CVSS score of CVE-2023-25136?
How do I remediate CVE-2023-25136?
Dependency Blast Radius
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