CVE-2019-12521

MEDIUMNVD 5.95.9—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.9 under NVD CVSS v3. EPSS exploit probability: 5.8%, top 8% 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
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 6%CVSS: 5.9Exploit: None knownExposed: 0

A fix is available — apply it.

An issue was discovered in Squid through 4.7. When Squid is parsing ESI, it keeps the ESI elements in ESIContext. ESIContext contains a buffer for holding a stack of ESIElements. When a new ESIElement is parsed, it is added via addStackElement. addStackElement has a check for the number of elements in this buffer, but it's off by 1, leading to a Heap Overflow of 1 element. The overflow is within the same structure so it can't affect adjacent memory blocks, and thus just leads to a crash while processing.

CVSS v3
5.9
EG Score
5.9(medium)
EG Risk
33(Track)
EG Risk 33/100SSVC: 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
Severity59% × 45%
Exploitation6% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
6%
EPSS %ILE
93%
KEV
Not listed

Published

April 15, 2020

Last Modified

November 21, 2024

References (16)

Vendor Advisories for CVE-2019-12521(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatsquid:4-8030020200828070549.30b713e62020-11-04redhat

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

(9 across 9 ecosystems)
Alpine:v3.10(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-r0—
Alpine:v3.11(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-r0—
Alpine:v3.9(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-r0—
Debian:10(1)
PackageVulnerable rangeFixed inDependents
squid4.6-1, 4.6-1+deb10u14.6-1+deb10u2—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
squid—4.11-1—
Debian:9(1)
PackageVulnerable rangeFixed inDependents
squid33.5.23-5, 3.5.23-5+deb9u13.5.23-5+deb9u2—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 5× in last 7d / 25× 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.

Showing the most recent 100 of 125 total refreshes for this CVE.

  1. 2026-08-25 13:45 UTCEPSS rescore
  2. 2026-08-21 23:45 UTCEPSS rescore
  3. 2026-08-20 23:45 UTCOSV refresh
  4. 2026-08-20 22:51 UTCEPSS rescore
  5. 2026-08-19 17:00 UTCEPSS rescore
  6. 2026-08-18 13:44 UTCEPSS rescore
  7. 2026-08-16 14:52 UTCEPSS rescore
  8. 2026-08-16 02:10 UTCEPSS rescore
  9. 2026-08-15 01:26 UTCEPSS rescore
  10. 2026-08-13 21:56 UTCEPSS rescore
  11. 2026-08-12 13:47 UTCEPSS rescore
  12. 2026-08-09 13:43 UTCEPSS rescore
  13. 2026-08-08 16:33 UTCEPSS rescore
  14. 2026-08-07 16:23 UTCEPSS rescore
  15. 2026-08-06 13:43 UTCEPSS rescore
  16. 2026-08-05 19:13 UTCEPSS rescore
  17. 2026-08-05 15:11 UTCOSV refresh
  18. 2026-08-04 15:05 UTCEPSS rescore
  19. 2026-08-04 10:33 UTCEPSS rescore
  20. 2026-08-03 10:31 UTCEPSS rescore
  21. 2026-08-02 02:23 UTCEPSS rescore
  22. 2026-08-01 04:12 UTCEPSS rescore
  23. 2026-07-30 16:24 UTCEPSS rescore
  24. 2026-07-30 01:27 UTCEPSS rescore
  25. 2026-07-28 15:32 UTCEPSS rescore
Show 75 more
  1. 2026-07-26 14:51 UTCEPSS rescore
  2. 2026-07-25 14:14 UTCEPSS rescore
  3. 2026-07-24 14:14 UTCEPSS rescore
  4. 2026-07-24 14:14 UTCEPSS rescore
  5. 2026-07-23 14:15 UTCEPSS rescore
  6. 2026-07-23 01:39 UTCEG score recompute
  7. 2026-07-22 22:19 UTCEG score recompute
  8. 2026-07-22 14:05 UTCEPSS rescore
  9. 2026-07-21 15:22 UTCEPSS rescore
  10. 2026-07-21 15:22 UTCEPSS rescore
  11. 2026-07-20 17:04 UTCEPSS rescore
  12. 2026-07-19 14:28 UTCEPSS rescore
  13. 2026-07-19 14:28 UTCEPSS rescore
  14. 2026-07-19 14:24 UTCOSV refresh
  15. 2026-07-19 02:26 UTCEPSS rescore
  16. 2026-07-19 02:26 UTCEPSS rescore
  17. 2026-07-18 10:01 UTCEPSS rescore
  18. 2026-07-16 16:59 UTCEPSS rescore
  19. 2026-07-16 16:59 UTCEPSS rescore
  20. 2026-07-15 16:55 UTCEPSS rescore
  21. 2026-07-13 22:27 UTCEPSS rescore
  22. 2026-07-13 06:10 UTCEPSS rescore
  23. 2026-07-13 06:10 UTCEPSS rescore
  24. 2026-07-12 05:43 UTCEPSS rescore
  25. 2026-07-11 08:24 UTCEPSS rescore
  26. 2026-07-09 19:06 UTCEPSS rescore
  27. 2026-07-08 15:11 UTCEPSS rescore
  28. 2026-07-07 13:42 UTCEPSS rescore
  29. 2026-07-06 16:25 UTCEPSS rescore
  30. 2026-07-06 02:20 UTCEPSS rescore
  31. 2026-07-05 02:27 UTCEPSS rescore
  32. 2026-07-04 06:28 UTCEPSS rescore
  33. 2026-07-04 06:28 UTCEPSS rescore
  34. 2026-07-02 16:56 UTCEPSS rescore
  35. 2026-07-02 00:25 UTCOSV refresh
  36. 2026-07-01 15:03 UTCEPSS rescore
  37. 2026-07-01 15:03 UTCEPSS rescore
  38. 2026-06-30 23:20 UTCEPSS rescore
  39. 2026-06-30 23:20 UTCEPSS rescore
  40. 2026-06-28 04:54 UTCEPSS rescore
  41. 2026-06-28 04:53 UTCEPSS rescore
  42. 2026-06-27 03:06 UTCEPSS rescore
  43. 2026-06-27 03:06 UTCEPSS rescore
  44. 2026-06-25 13:47 UTCEPSS rescore
  45. 2026-06-25 13:47 UTCEPSS rescore
  46. 2026-06-24 14:03 UTCEPSS rescore
  47. 2026-06-24 14:02 UTCEPSS rescore
  48. 2026-06-23 21:30 UTCEPSS rescore
  49. 2026-06-23 21:30 UTCEPSS rescore
  50. 2026-06-22 14:23 UTCEPSS rescore
  51. 2026-06-22 14:23 UTCEPSS rescore
  52. 2026-06-21 14:54 UTCEPSS rescore
  53. 2026-06-21 14:54 UTCEPSS rescore
  54. 2026-06-21 01:57 UTCEPSS rescore
  55. 2026-06-21 01:57 UTCEPSS rescore
  56. 2026-06-19 19:23 UTCEPSS rescore
  57. 2026-06-19 19:23 UTCEPSS rescore
  58. 2026-06-18 17:50 UTCEPSS rescore
  59. 2026-06-17 17:50 UTCEPSS rescore
  60. 2026-06-16 17:50 UTCEPSS rescore
  61. 2026-06-15 17:45 UTCEPSS rescore
  62. 2026-06-14 23:15 UTCEPSS rescore
  63. 2026-06-14 23:15 UTCEPSS rescore
  64. 2026-06-14 04:43 UTCOSV refresh
  65. 2026-06-13 22:58 UTCEPSS rescore
  66. 2026-06-12 23:09 UTCEPSS rescore
  67. 2026-06-11 13:58 UTCEPSS rescore
  68. 2026-06-11 13:58 UTCEPSS rescore
  69. 2026-06-10 22:16 UTCEPSS rescore
  70. 2026-06-10 13:19 UTCEPSS rescore
  71. 2026-06-08 14:15 UTCEPSS rescore
  72. 2026-06-08 14:14 UTCEPSS rescore
  73. 2026-06-07 15:23 UTCEPSS rescore
  74. 2026-06-07 15:22 UTCEPSS rescore
  75. 2026-06-06 13:45 UTCEPSS rescore

Frequently asked(5)

What is CVE-2019-12521?
CVE-2019-12521 is a medium vulnerability published on April 15, 2020. An issue was discovered in Squid through 4.7. When Squid is parsing ESI, it keeps the ESI elements in ESIContext. ESIContext contains a buffer for holding a stack of ESIElements. When a new ESIElement is parsed, it is added via addStackElement. addStackElement has a check for the number of elements…
When was CVE-2019-12521 disclosed?
CVE-2019-12521 was first published in the National Vulnerability Database on April 15, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2019-12521 actively exploited?
CVE-2019-12521 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 6% probability of exploitation in the next 30 days, which ranks it in the top 7.5% of all scored CVEs.
What is the CVSS score of CVE-2019-12521?
CVE-2019-12521 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2019-12521?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2019-12521, 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.

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