LiveActive security incident?Get immediate response
CVE Record

CVE-2026-31640: rxrpc: Fix use of wrong skb when comparing queued RESP challenge serial

In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix use of wrong skb when comparing queued RESP challenge serial In rxrpc_post_response(), the code should be comparing the challenge serial number from the cached response before deciding to switch to a newer response, but looks at the newer packet private data instead, rendering the comparison always false. Fix this by switching to look at the older packet. Fix further[1] to substitute the new packet in place of the old one if newer and also to release whichever we don't use.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

A Linux kernel RxRPC flaw mishandles authentication challenge responses by comparing data from the wrong network packet. The supplied CVSS rates it 7.5 because a network-accessible attacker may cause an availability impact without credentials or user interaction. The sources do not describe the exact failure mechanism or confirm real-world exploitation.

Executive priority

Treat this as a high-priority availability issue for Linux systems using RxRPC, especially externally reachable or business-critical hosts. Accelerate vendor-version verification and patching, while avoiding assumptions that every Linux system is exposed. There is currently no supplied evidence of active exploitation.

Technical view

In rxrpc_post_response(), the kernel reads the newer skb's private data instead of the cached response when comparing challenge serial numbers, making the comparison always false. The fix reads the older skb, retains the newer response when appropriate, and releases the unused packet. The supplied record characterizes impact as availability only.

Likely exposure

Potential exposure is limited to affected Linux kernels where the RxRPC code path is present and reachable. The bundle lists versions including 6.16, 6.18.23, 6.19.13, and 7.0, but contains ambiguous version data. Exact distribution package and backport status must be verified with the Linux vendor.

Exploitation context

The supplied CVSS vector indicates remote, low-complexity, unauthenticated exploitation requiring no user interaction, with high availability impact. However, CVE-2026-31640 is not identified as KEV, and the supplied sources provide no evidence of active exploitation, public proof-of-concept code, or observed attacks.

Researcher notes

The record does not provide a CWE, triggering packet sequence, crash trace, affected distribution mapping, or detailed availability mechanism. Analysis should remain focused on the incorrect skb selection and response replacement logic. The duplicated commit identifiers and unusual affected-version entry "0" reduce confidence in precise version boundaries.

Mitigation direction

  • Obtain a vendor-supported kernel containing the applicable referenced stable fix.
  • Check distribution advisories for exact package versions and backport status.
  • Prioritize systems where RxRPC is enabled, used, or network-reachable.
  • Apply vendor-recommended temporary controls if immediate kernel replacement is unavailable.

Validation and detection

  • Record each system's running kernel and distribution package version.
  • Confirm whether the deployed kernel includes an applicable referenced fix commit.
  • Determine whether RxRPC is enabled and used in the system's workload.
  • Recheck vendor advisories because the supplied affected-version data is ambiguous.
  • Verify the updated kernel is running after remediation.
Prepared
Confidence
medium
Sources
5

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.

cve · low confidence lookup

CVE-2026-31640 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
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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.

1CVSS vectors
3Timeline events
0ADP providers
4Source links

CVSS vector scores

1 official score

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6Linux

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-31640Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
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. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

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

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux5800b1cf3fd8ccab752a101865be1e76dac33142, 5800b1cf3fd8ccab752a101865be1e76dac33142, 5800b1cf3fd8ccab752a101865be1e76dac33142unaffected
LinuxLinux6.16, 0, 6.18.23, 6.19.13, 7.0affected
Weakness

CWE details

No CWE listed

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