The RC4 algorithm, as used in the TLS protocol and SSL protocol, has many single-byte biases, which makes it easier for remote attackers to conduct plaintext-recovery attacks via statistical analysis of ciphertext in a large number of sessions that use the same plaintext.
CVE-2013-2566
“▲” beside the score: it is higher than NVD's CVSS score.
Score elevated to 9.0 because EPSS predicted 84% probability of exploitation within the next 30 days (99th percentile of EPSS-scored CVEs) when EchelonGraph scored this CVE. NVD baseline CVSS 5.9 retained for reference. Confidence: see factors.
Also known asEUVD-2013-2508 (ENISA EUVD) · GHSA-f67x-vqh9-8p43 (GitHub Security Advisories)Source: ENISA EUVD
- High exploitation likelihood — EPSS 84%
- Public exploit code is available (Metasploit)
A fix is available — apply it.
- CVSS v3
- 5.9
- EG Score
- 9.0CRITICALhigh confidence
- EG Risk
- 60EG Risk 60/100
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)Severity59% × 45%Impact severity (EG Severity): CVSS 5.9 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation84% × 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
- 84%
- 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 (9.0): severity, escalated by confirmed exploitation. This CVE's 9.0 is EPSS's lift toward 9.0 from its impact severity (EG Severity, CVSS 5.9 MEDIUM): a likelihood of exploitation, not impact.
- EG Severity
- 5.9 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 84% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). 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
March 15, 2013
Last Modified
May 22, 2026
Advisory Details (5)
Auto-updated May 29, 2026Mozilla Network Security Service: Multiple vulnerabilities (GLSA 201406-19) — Gentoo security
http://security.gentoo.org/glsa/glsa-201406-19.xmlThe Opera Blog - News | Opera
http://my.opera.com/securitygroup/blog/2013/03/20/on-the-precariousness-of-rc4'[security bulletin] HPSBGN03324 rev.1 - HP Business Service Automation Essentials Core, Remote Discl' - MARC
http://marc.info/?l=bugtraq&m=143039468003789&w=2Attack of the week: RC4 is kind of broken in TLS – A Few Thoughts on Cryptographic Engineering
http://blog.cryptographyengineering.com/2013/03/attack-of-week-rc4-is-kind-of-broken-in.htmlPatch Availability(2)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| ubuntu | thunderbird (1:24.1.1+build1-0ubuntu0.13.10.1) @ saucy | 2026-11-02 | ubuntu |
| ubuntu | firefox (25.0.1+build1-0ubuntu0.12.10.1) @ quantal | 2026-11-02 | ubuntu |
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.
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
All Vendor Advisories
(2)
Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.
Data Freshness Timeline
(refreshed 24× in last 7d / 70× 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 98 of 131 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. 2 repeat rows among the latest 100 are merged into the row they repeat. The 33 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-11-02 13:06 UTCEG score recompute
- 2026-11-02 13:06 UTCVendor advisory
- 2026-11-02 13:06 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub severity MODERATE · GitHub CVSS 5.9
- 2026-11-01 14:18 UTCEG score recompute
- 2026-11-01 14:18 UTCVendor advisory
- 2026-11-01 14:18 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub severity MODERATE · GitHub CVSS 5.9
- 2026-10-31 15:33 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-30 16:46 UTCEG score recompute
- 2026-10-30 16:46 UTCVendor advisory
- 2026-10-30 16:46 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-30 16:27 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-29 18:00 UTCEG score recompute
- 2026-10-29 18:00 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-29 17:59 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-28 19:11 UTCEG score recompute
- 2026-10-28 19:11 UTCVendor advisory
- 2026-10-28 19:11 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-28 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-27 20:07 UTCEG score recompute
- 2026-10-27 20:07 UTCVendor advisory
- 2026-10-27 20:07 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-27 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-26 21:21 UTCEG score recompute
- 2026-10-26 21:21 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-25 20:30 UTCVendor advisory
Show 73 moreShow fewer
- 2026-10-25 20:30 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-25 20:09 UTCEG score recompute
- 2026-10-25 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-24 21:44 UTCEG score recompute
- 2026-10-24 21:44 UTCVendor advisory
- 2026-10-24 21:44 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-23 22:59 UTCEG score recompute
- 2026-10-23 22:59 UTCVendor advisory
- 2026-10-23 22:58 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-22 23:41 UTCEG score recompute
- 2026-10-22 23:41 UTCVendor advisory
- 2026-10-22 23:41 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-22 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-22 00:55 UTCEG score recompute
- 2026-10-22 00:55 UTCVendor advisory
- 2026-10-22 00:54 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-21 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-21 02:09 UTCEG score recompute
- 2026-10-21 02:08 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-20 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-20 03:21 UTCEG score recompute
- 2026-10-20 03:20 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-19 03:46 UTCEG score recompute
- 2026-10-19 03:45 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-18 04:58 UTCEG score recompute
- 2026-10-18 04:58 UTCVendor advisory
- 2026-10-18 04:58 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-17 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-17 05:30 UTCEG score recompute
- 2026-10-17 05:29 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-16 06:40 UTCEG score recompute
- 2026-10-16 06:40 UTCVendor advisory
- 2026-10-16 06:40 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-15 05:21 UTCEG score recompute
- 2026-10-15 05:21 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-14 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-14 01:02 UTCEG score recompute
- 2026-10-14 01:02 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-13 16:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-12 21:10 UTCEG score recompute
- 2026-10-12 21:10 UTCVendor advisory
- 2026-10-12 21:10 UTCGHSA enrichmentGHSA-f67x-vqh9-8p43 · GitHub CVSS 5.9
- 2026-10-12 01:32 UTCEG score recompute
- 2026-10-09 20:00 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-10-06 15:10 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-30 00:10 UTCEG score recompute
- 2026-09-27 13:39 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-26 15:52 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-24 13:57 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-18 19:21 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-07 15:56 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-06 13:42 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-05 15:22 UTCEPSS rescoreEPSS 78% · 99th percentile
- 2026-09-04 13:55 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-09-02 14:06 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-27 14:20 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-26 14:40 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-24 07:23 UTCEPSS rescoreEPSS 78% · 99th percentile
- 2026-08-21 23:44 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-19 16:59 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-16 02:09 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-15 01:25 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-12 13:45 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-08-07 16:21 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-30 01:26 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-28 15:31 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-23 01:10 UTCEG score recompute
- 2026-07-23 00:13 UTCEG score recompute▲ 3.10
- 2026-07-22 21:51 UTCEG score recompute▼ 3.10
- 2026-07-22 14:04 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-21 15:21 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-18 10:00 UTCEPSS rescoreEPSS 84% · 99th percentile
- 2026-07-15 16:54 UTCEPSS rescoreEPSS 84% · 99th percentile
Publicly available exploits
(1 reference)Public exploit code is referenced for this CVE (1 Metasploit module). Defenders should treat patch urgency accordingly.
- Metasploitauxiliary/scanner/ssl/ssl_version✓ verifiedPublished Oct 17, 2014
SSL/TLS Version Detection
Open source ↗
Related CVEs(same vendor + same CWE)
Same vendor
3 shownubuntu:USN-2031-1
Same CWE
10 shownCWE-326 · CWE-327
- CVE-2013-0764EG 9.3HIGH
- CVE-2012-4571CVSS v2 2.1EG 7.5HIGH
- CVE-2012-5575EG 6.4EPSS p94MEDIUM
- CVE-2012-3458CVSS v2 4.3EG 5.3MEDIUM
- CVE-2012-2146CVSS v2 4.3EG 7.5HIGH
- CVE-2007-6755EG 5.8MEDIUM
- CVE-2013-4508EG 7.5HIGH
- CVE-2014-1491EG 4.3EPSS p92MEDIUM
- CVE-2013-6372EG 2.1LOW
- CVE-2014-0224NVD 7.4EG 9.0EPSS p100CRITICAL
Frequently asked(5)
What is CVE-2013-2566?
When was CVE-2013-2566 made public?
Is CVE-2013-2566 actively exploited?
What is the CVSS score of CVE-2013-2566?
How do I remediate CVE-2013-2566?
Dependency Blast Radius
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