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CVE Record

CVE-2026-39979: jq: Out-of-Bounds Read in jv_parse_sized() Error Formatting for Non-NUL-Terminated Counted Buffers

jq is a command-line JSON processor. In commits before 2f09060afab23fe9390cce7cb860b10416e1bf5f, the jv_parse_sized() API in libjq accepts a counted buffer with an explicit length parameter, but its error-handling path formats the input buffer using %s in jv_string_fmt(), which reads until a NUL terminator is found rather than respecting the caller-supplied length. This means that when malformed JSON is passed in a non-NUL-terminated buffer, the error construction logic performs an out-of-bounds read past the end of the buffer. The vulnerability is reachable by any libjq consumer calling jv_parse_sized() with untrusted input, and depending on memory layout, can result in memory disclosure or process termination. The issue has been patched in commit 2f09060afab23fe9390cce7cb860b10416e1bf5f.

HighCVSS 8.2Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-39979 is a jq/libjq memory-read bug triggered during malformed JSON error handling. A vulnerable library consumer may read past the provided input buffer, causing a crash or limited memory disclosure. Business urgency is highest where applications expose libjq parsing to untrusted network input.

Executive priority

Treat as a high-priority patching and exposure-discovery item, especially for internet-facing services embedding libjq. The risk is conditional, but the published CVSS is high and remediation is available in upstream and Red Hat sources.

Technical view

Before commit 2f09060afab23fe9390cce7cb860b10416e1bf5f, libjq jv_parse_sized() accepted explicit buffer lengths but formatted malformed input with %s during error construction. Non-NUL-terminated counted buffers can cause an out-of-bounds read. The issue is CWE-125 with CVSS 3.1 score 8.2, affecting jq before the fixing commit.

Likely exposure

Exposure is most likely in applications embedding libjq and calling jv_parse_sized() on untrusted JSON. The bundle does not prove every jq command-line use is exploitable. Red Hat advisories indicate packaged remediation exists, but product-level applicability should be verified per environment.

Exploitation context

The source bundle does not cite active exploitation, and KEV is false. Exploitation depends on a consumer passing malformed, non-NUL-terminated untrusted input to jv_parse_sized(). Impact may be process termination or limited adjacent memory disclosure, depending on memory layout.

Researcher notes

Key condition is malformed JSON in a non-NUL-terminated counted buffer passed to jv_parse_sized(). Focus review on libjq API consumers, not only direct jq CLI invocations. Avoid assuming exploitability without confirming buffer ownership, termination, and input trust boundaries.

Mitigation direction

  • Upgrade jq/libjq to a build containing commit 2f09060afab23fe9390cce7cb860b10416e1bf5f.
  • Apply relevant Red Hat errata for systems using Red Hat-packaged jq or libjq.
  • Inventory applications that embed libjq and parse untrusted JSON.
  • Prioritize externally reachable services using jv_parse_sized() on attacker-controlled input.
  • If no vendor package is available, check vendor guidance before choosing local backports.

Validation and detection

  • Check installed jq/libjq versions and package advisories against CVE-2026-39979.
  • Confirm whether applications call jv_parse_sized() with untrusted counted buffers.
  • Review SBOMs and dependency manifests for bundled or statically linked libjq.
  • Validate patched builds include commit 2f09060afab23fe9390cce7cb860b10416e1bf5f.
  • Confirm relevant Red Hat errata are applied where applicable.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-125: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-39979 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.2 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
33Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.2CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H3.94.2redhat-SADP
6.9CVSS 4.0MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N——GitHub_M

Vulnerability scoring details

Base CVSS 4.0 score

6.9Medium
CVSS 4.0 vector shape for CVE-2026-39979Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPjq: out-of-bounds read in jv_parse_sized() on error formatting for non-NUL-terminated buffers
other:Red Hat severity ratingcvssV3_1
  • 2026-04-13T23:01:01.219Z: Reported to Red Hat.
  • 2026-04-13T22:18:56.252Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
jqlangjq< 2f09060afab23fe9390cce7cb860b10416e1bf5fListed
Weakness

CWE details

CWE-125

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-125 · source CWE mapping

Out-of-bounds Read

Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs