CVE-2026-63476

MEDIUMPre-NVD 4.34.3
EchelonGraph scoreMEDIUM confidence

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

This medium-severity CVE scores 4.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3% (21st percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Elevated

Also known asEUVD-2026-116272 (ENISA EUVD)Source: ENISA EUVD

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: 0.3%CVSS: 4.3Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or man-in-the-middle-controlled remote can send one delta header that causes git.clone() or git.fetch() to allocate approximately 2 GB before validating the actual delta output. GitPackIndex.fromPack swallows the later size-mismatch error, so a host with sufficient memory may retain the resource waste without a visible failure, while containers, serverless functions, and small virtual machines may terminate. Node.js heap limits do not mitigate the off-heap Buffer allocation. This issue is fixed in version 1.38.6.

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
0.3%
EPSS %ILE
21st
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.a secondary CVSS source · CVSS v3.0 or v3.1
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-06). 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, and whom BOD 26-04 binds: 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.

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

November 3, 2026

Last Modified

November 7, 2026

Advisory Details (4)

Auto-updated Nov 7, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_commit, github_pr, github_release.
GitHub release Patch Available

v1.38.6

Patch available: isomorphic-git/isomorphic-git v1.38.6

https://github.com/isomorphic-git/isomorphic-git/releases/tag/v1.38.6
GitHub commit Patch Available

commit 823843d1cd19 (isomorphic-git/isomorphic-git)

Patch available: isomorphic-git/isomorphic-git v1.41.3 (contains commit 823843d1cd19)

https://github.com/isomorphic-git/isomorphic-git/commit/823843d1cd19182df79bc907c767f5bcecb39a0b
GitHub pull request Patch Available

fix: fixing git internals

Patch available: isomorphic-git/isomorphic-git v1.41.3 (PR #2370 merged 2026-06-30)

https://github.com/isomorphic-git/isomorphic-git/pull/2370
GitHub advisoryMentions a patch (unverified)🟡 PoC Available

Unbounded memory allocation from attacker-controlled delta target size (DoS) · Advisory · isomorphic-git/isomorphic-git · GitHub

https://github.com/isomorphic-git/isomorphic-git/security/advisories/GHSA-9x82-4j54-863h

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 11× 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 its CVE.org record (CNA or CISA ADP). 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). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.

  1. 2026-11-12 16:34 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  2. 2026-11-11 16:40 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  3. 2026-11-10 16:45 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  4. 2026-11-09 16:35 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  5. 2026-11-08 16:40 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  6. 2026-11-07 16:39 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  7. 2026-11-07 04:27 UTCEchelonGraph re-scored
  8. 2026-11-07 03:31 UTCEchelonGraph re-scored
  9. 2026-11-06 16:39 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  10. 2026-11-05 16:38 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  11. 2026-11-04 16:36 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  12. 2026-11-03 21:03 UTCENISA EUVD ID recordedEUVD-2026-116272 · Source: ENISA EUVD
  13. 2026-11-03 20:28 UTCEchelonGraph re-scored
  14. 2026-11-03 19:51 UTCEchelonGraph re-scoredFirst assessed: 4.3 MEDIUM
  15. 2026-11-03 19:51 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-63476?
CVE-2026-63476 is a medium-severity vulnerability; its CVE record was published on November 3, 2026. isomorphic-git is a pure JavaScript implementation of Git for Node.js and browsers. Prior to 1.38.6, isomorphic-git reads a server-controlled targetSize while applying a packfile delta in src/utils/applyDelta.js and passes it without a bound to Buffer.alloc(targetSize). A malicious or…
When was the CVE record for CVE-2026-63476 published?
The CVE record for CVE-2026-63476 was published on November 3, 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 November 7, 2026; the record at its source may have been updated since.
Is CVE-2026-63476 actively exploited?
CVE-2026-63476 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (21st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-63476?
CVE-2026-63476 has a CVSS base score of 4.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-63476?
A fix for CVE-2026-63476 is available: update to the fixed version the vendor names in its advisory.

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