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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-safety flaw. When certain malformed JSON is handled through a specific libjq API, jq can read beyond the provided input buffer while building an error message. The likely business impact is service crash, with possible limited memory disclosure in applications that embed vulnerable libjq.

Executive priority

Treat this as a high-priority patching item for systems embedding jq/libjq in network-facing or automated JSON-processing workflows. It is not currently supported by the provided sources as actively exploited, but the unauthenticated, low-complexity availability risk justifies timely remediation.

Technical view

The issue is a CWE-125 out-of-bounds read in jv_parse_sized(). The API accepts an explicit buffer length, but the error path formats the input with %s, causing reads until a NUL byte rather than the supplied length. Sources rate it CVSS 8.2 with low confidentiality and high availability impact.

Likely exposure

Exposure is most likely in applications or services that embed libjq and call jv_parse_sized() on untrusted JSON. The source bundle identifies jq versions before commit 2f09060afab23fe9390cce7cb860b10416e1bf5f as affected. Red Hat advisories indicate downstream package handling exists, but product-specific status must be checked in vendor guidance.

Exploitation context

The bundle does not show CISA KEV listing or active exploitation. Exploitability depends on a libjq consumer passing malformed, untrusted JSON in a non-NUL-terminated counted buffer. The documented outcomes are memory disclosure depending on layout or process termination; no integrity impact is stated.

Researcher notes

The narrow trigger condition matters: malformed JSON, jv_parse_sized(), and a non-NUL-terminated counted buffer. The patch changes the vulnerable error-formatting behavior. Available evidence supports out-of-bounds read impact, not code execution. Validate exposure in consumers, not only standalone jq command availability.

Mitigation direction

  • Update jq/libjq to a build containing commit 2f09060afab23fe9390cce7cb860b10416e1bf5f.
  • Apply relevant vendor packages or errata for deployed operating systems.
  • Prioritize services that parse untrusted JSON through embedded libjq.
  • If patching is delayed, follow vendor guidance and reduce untrusted libjq parsing exposure.
  • Track Red Hat advisories for affected downstream package status.

Validation and detection

  • Inventory jq binaries, libjq libraries, and statically embedded jq copies.
  • Confirm installed builds include commit 2f09060afab23fe9390cce7cb860b10416e1bf5f or vendor fixes.
  • Review code for jv_parse_sized() use with untrusted input.
  • Identify services where malformed JSON reaches libjq error handling.
  • Check Red Hat CVE and errata pages for platform-specific applicability.
Prepared
Confidence
high
Sources
10

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.

Open ATT&CK lookup
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