CVE-2026-27205

MEDIUMNVD 4.34.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.3 under NVD CVSS v3. EPSS exploit probability: 0.3%, top 73% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
4.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 4.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache the response, as it may contain information specific to a logged in user. This is handled in most cases, but some forms of access such as the Python in operator were overlooked. The severity and risk depend on the application being hosted behind a caching proxy that doesn't ignore responses with cookies, not setting a Cache-Control header to mark pages as private or non-cacheable, and accessing the session in a way that only touches keys without reading values or mutating the session. The issue has been fixed in version 3.1.3.

CVSS v3
4.3
EG Score
4.3(medium)
EG Risk
24(Track)
EG Risk 24/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity43% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
28%
KEV
Not listed

Published

February 21, 2026

Last Modified

June 17, 2026

Advisory Details (3)

Auto-updated Aug 7, 2026
Patch available. Sources: github_commit, github_release, github.
github Patch Available

Flask session does not add `Vary: Cookie` header when accessed in some ways · Advisory · pallets/flask · GitHub

https://github.com/pallets/flask/security/advisories/GHSA-68rp-wp8r-4726
github_release Patch Available

Release 3.1.3 (pallets/flask)

Patch available: pallets/flask 3.1.3

https://github.com/pallets/flask/releases/tag/3.1.3
github_commit Patch Available

commit 089cb86dd22b (pallets/flask)

Patch available: pallets/flask 3.1.3 (contains commit 089cb86dd22b)

https://github.com/pallets/flask/commit/089cb86dd22bff589a4eafb7ab8e42dc357623b4

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
flask1.1.2-2 ... 3.1.3-4 (25 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
flask2.2.2-3 ... 3.1.3-4 (14 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
flask3.1.1-1 ... 3.1.3-4 (7 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
flask3.1.1-1, 3.1.2-13.1.3-1—
PyPI(1)
PackageVulnerable rangeFixed inDependents
flask0.1 ... 3.1.2 (63 versions)3.1.3—

Weakness Classification(1)

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

All Vendor Advisories

(1)

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 7× in last 7d / 28× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. 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. Most recent first.

  1. 2026-09-18 20:06 UTCOSV refresh
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 19:27 UTCEPSS rescore
  4. 2026-09-17 19:30 UTCEPSS rescore
  5. 2026-09-16 14:08 UTCEPSS rescore
  6. 2026-09-16 05:15 UTCEPSS rescore
  7. 2026-09-13 16:47 UTCEPSS rescore
  8. 2026-09-12 15:01 UTCEPSS rescore
  9. 2026-09-11 14:52 UTCEPSS rescore
  10. 2026-09-10 09:34 UTCEPSS rescore
  11. 2026-09-08 22:00 UTCEPSS rescore
  12. 2026-09-07 16:01 UTCEPSS rescore
  13. 2026-09-06 13:47 UTCEPSS rescore
  14. 2026-09-06 13:47 UTCEPSS rescore
  15. 2026-09-04 05:06 UTCEPSS rescore
  16. 2026-09-02 14:11 UTCEPSS rescore
  17. 2026-09-01 13:53 UTCEPSS rescore
  18. 2026-09-01 04:39 UTCEPSS rescore
  19. 2026-08-30 23:03 UTCOSV refresh
  20. 2026-08-30 19:17 UTCEPSS rescore
  21. 2026-08-30 01:22 UTCEPSS rescore
  22. 2026-08-28 21:41 UTCEPSS rescore
  23. 2026-08-27 14:25 UTCEPSS rescore
  24. 2026-08-26 14:46 UTCEPSS rescore
  25. 2026-08-25 13:48 UTCEPSS rescore
Show 41 more
  1. 2026-08-23 00:19 UTCEPSS rescore
  2. 2026-08-21 23:49 UTCEPSS rescore
  3. 2026-08-20 22:55 UTCEPSS rescore
  4. 2026-08-19 17:03 UTCEPSS rescore
  5. 2026-08-18 13:48 UTCEPSS rescore
  6. 2026-08-17 13:47 UTCEPSS rescore
  7. 2026-08-16 14:56 UTCEPSS rescore
  8. 2026-08-16 02:14 UTCEPSS rescore
  9. 2026-08-15 01:30 UTCEPSS rescore
  10. 2026-08-14 09:17 UTCEG score recompute
  11. 2026-08-14 09:17 UTCVendor advisory
  12. 2026-08-13 22:00 UTCEPSS rescore
  13. 2026-08-13 03:04 UTCEG score recompute
  14. 2026-08-13 03:04 UTCVendor advisory
  15. 2026-08-12 13:50 UTCEPSS rescore
  16. 2026-08-12 01:29 UTCEG score recompute
  17. 2026-08-12 01:29 UTCVendor advisory
  18. 2026-08-11 13:42 UTCEPSS rescore
  19. 2026-08-11 00:00 UTCEPSS rescore
  20. 2026-08-10 10:32 UTCEG score recompute
  21. 2026-08-10 10:32 UTCVendor advisory
  22. 2026-08-09 13:46 UTCEPSS rescore
  23. 2026-08-09 08:55 UTCEG score recompute
  24. 2026-08-09 08:55 UTCVendor advisory
  25. 2026-08-08 16:37 UTCEPSS rescore
  26. 2026-08-07 21:04 UTCEG score recompute
  27. 2026-08-07 21:04 UTCVendor advisory
  28. 2026-08-06 13:46 UTCEPSS rescore
  29. 2026-08-06 03:15 UTCEG score recompute
  30. 2026-08-06 03:15 UTCVendor advisory
  31. 2026-08-05 19:17 UTCEPSS rescore
  32. 2026-08-04 15:10 UTCEPSS rescore
  33. 2026-08-03 10:36 UTCEPSS rescore
  34. 2026-08-02 19:51 UTCEG score recompute
  35. 2026-08-02 19:51 UTCVendor advisory
  36. 2026-08-02 02:26 UTCEPSS rescore
  37. 2026-08-01 04:16 UTCEPSS rescore
  38. 2026-07-30 16:27 UTCEPSS rescore
  39. 2026-07-30 01:30 UTCEPSS rescore
  40. 2026-07-28 15:36 UTCEPSS rescore
  41. 2026-07-27 14:10 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-27205?
CVE-2026-27205 is a medium vulnerability published on February 21, 2026. Flask is a web server gateway interface (WSGI) web application framework. In versions 3.1.2 and below, when the session object is accessed, Flask should set the Vary: Cookie header., resulting in a Use of Cache Containing Sensitive Information vulnerability. The logic instructs caches not to cache…
When was CVE-2026-27205 disclosed?
CVE-2026-27205 was first published in the National Vulnerability Database on February 21, 2026, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-27205 actively exploited?
CVE-2026-27205 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 72.0% of all scored CVEs.
What is the CVSS score of CVE-2026-27205?
CVE-2026-27205 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2026-27205?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-27205, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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