CVE-2026-33635

MEDIUMNVD 4.34.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This medium-severity CVE scores 4.3 under NVD CVSS v3. EPSS exploit probability: 0.4% (30th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
Elevated
4.3EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 4.3Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding arbitrary calendar lines to the output. Icalendar::Values::Uri falls back to the raw input string when URI.parse fails and later serializes it with value.to_s without removing or escaping \r or \n characters. That value is embedded directly into the final ICS line by the normal serializer, so a payload containing CRLF can terminate the original property and create a new ICS property or component. (It looks like you can inject via url, source, image, organizer, attach, attendee, conference, tzurl because of this). Applications that generate .ics files from partially untrusted metadata are impacted. As a result, downstream calendar clients or importers may process attacker-supplied content as if it were legitimate event data, such as added attendees, modified URLs, alarms, or other calendar fields. Version 2.12.2 contains a patch for the issue.

CVSS v3
4.3
EG Score
4.3MEDIUMmedium confidence
EG Risk
35
EG Risk 35/100

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)
Severity43% × 45%
Impact severity (EG Severity): CVSS 4.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
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
0.4%
EPSS %ILE
30th
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 (4.3): severity, escalated by confirmed exploitation. This CVE's 4.3 is its impact severity (EG Severity), not escalated.

EG Severity
4.3 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-17). 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

March 26, 2026

Last Modified

June 17, 2026

Advisory Details (3)

Auto-updated Aug 9, 2026
Patch available. Sources: github_commit, github.
Web page

ruby-advisory-db/gems/icalendar/CVE-2026-33635.yml at master · rubysec/ruby-advisory-db · GitHub

https://github.com/rubysec/ruby-advisory-db/blob/master/gems/icalendar/CVE-2026-33635.yml
GitHub advisoryMentions a patch (unverified)

ics injection via unsanitized URI property values · Advisory · icalendar/icalendar · GitHub

https://github.com/icalendar/icalendar/security/advisories/GHSA-pv9c-9mfh-hvxq
GitHub commit

commit b8d23b490363 (icalendar/icalendar)

Fix landed in icalendar/icalendar commit b8d23b490363 — awaiting tagged release

https://github.com/icalendar/icalendar/commit/b8d23b490363ee5fffaec1d269a8618a912ca265

Affected Packages

(3 across 3 ecosystems)
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
ruby-icalendar2.10.0-1, 2.10.3-1, 2.4.1-2, 2.7.1-1, 2.8.0-1
  • every version on: no fix on record
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
ruby-icalendar2.10.0-1, 2.10.3-1, 2.8.0-1
  • every version on: no fix on record
—
RubyGems(1)
PackageVulnerable rangeFix by version rangeDependents
icalendar2.0.0 ... 2.9.0 (30 versions)
  • 2.0.0 up to 2.12.2: fixed in 2.12.2
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 8× in last 7d / 31× 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 95 of 196 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. 5 repeat rows among the latest 100 are merged into the row they repeat. The 101 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.4% · 30th percentile
  2. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  3. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  4. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  5. 2026-10-18 03:46 UTCEG score recompute
  6. 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  7. 2026-10-16 16:41 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  8. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  9. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  10. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  11. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  12. 2026-10-12 16:13 UTCEG score recompute
  13. 2026-10-11 19:55 UTCEG score recompute
  14. 2026-10-11 17:08 UTCEG score recompute
  15. 2026-10-11 14:35 UTCEG score recompute
  16. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  17. 2026-10-11 04:31 UTCOSV refresh
  18. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  19. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  20. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  21. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  22. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  23. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  24. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  25. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.4% · 28th percentile
Show 70 more
  1. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  2. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  3. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  4. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  5. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  6. 2026-09-26 00:26 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  7. 2026-09-21 16:19 UTCOSV refresh
  8. 2026-09-20 20:15 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  9. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  10. 2026-09-17 19:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  11. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  12. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  13. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  14. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  15. 2026-09-12 15:01 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  16. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  17. 2026-09-11 09:37 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  18. 2026-09-10 09:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  19. 2026-09-08 22:00 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  20. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  21. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  22. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  23. 2026-09-02 14:11 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  24. 2026-09-02 13:26 UTCOSV refresh
  25. 2026-09-01 13:53 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  26. 2026-09-01 04:39 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  27. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  28. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  29. 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  30. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  31. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  32. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  33. 2026-08-24 14:17 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  34. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  35. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  36. 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  37. 2026-08-19 17:03 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  38. 2026-08-18 13:48 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  39. 2026-08-17 13:47 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  40. 2026-08-16 14:56 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  41. 2026-08-16 10:05 UTCEG score recompute
  42. 2026-08-16 02:14 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  43. 2026-08-15 01:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  44. 2026-08-14 06:23 UTCEG score recompute
  45. 2026-08-13 22:00 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  46. 2026-08-12 20:40 UTCEG score recompute
  47. 2026-08-12 13:50 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  48. 2026-08-11 04:01 UTCEG score recompute
  49. 2026-08-11 00:00 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  50. 2026-08-10 04:59 UTCEG score recompute
  51. 2026-08-09 13:46 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  52. 2026-08-09 05:56 UTCEG score recompute
  53. 2026-08-08 16:37 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  54. 2026-08-07 16:22 UTCEG score recompute
  55. 2026-08-06 13:46 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  56. 2026-08-06 00:50 UTCEG score recompute
  57. 2026-08-05 19:17 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  58. 2026-08-04 15:10 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  59. 2026-08-04 10:38 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  60. 2026-08-03 23:15 UTCEG score recompute
  61. 2026-08-03 10:36 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  62. 2026-08-02 15:20 UTCEG score recompute
  63. 2026-08-02 02:27 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  64. 2026-08-01 04:16 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  65. 2026-07-30 16:28 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  66. 2026-07-30 01:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  67. 2026-07-27 14:13 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  68. 2026-07-26 14:54 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  69. 2026-07-25 14:18 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  70. 2026-07-24 14:17 UTCEPSS rescoreEPSS 0.2% · 15th percentile

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-33635?
CVE-2026-33635 is a medium-severity vulnerability; its CVE record was published on March 26, 2026. iCalendar is a Ruby library for dealing with iCalendar files in the iCalendar format defined by RFC-5545. Starting in version 2.0.0 and prior to version 2.12.2, .ics serialization does not properly sanitize URI property values, enabling ICS injection through attacker-controlled input, adding…
When was the CVE record for CVE-2026-33635 published?
The CVE record for CVE-2026-33635 was published on March 26, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of June 17, 2026; the record at its source may have been updated since.
Is CVE-2026-33635 actively exploited?
CVE-2026-33635 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (30th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-33635?
CVE-2026-33635 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2026-33635?
A fix for CVE-2026-33635 is available: update to the fixed version the vendor names in its advisory.

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