Linux Kernel: 3 memory flaws used in attacks
OFFICIAL NAMES: Linux Kernel Out-of-Bounds Write Vulnerability · Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability · Linux Kernel Race Condition Vulnerability
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TECHNICAL SUMMARY Linux Kernel contains an improper check for unusual or exceptional conditions vulnerability in the TLS receive path which allows a zero-length record retrieved from the rx_list to bypass the intended recvmsg() record-type handling, potentially causing subsequent TLS records to be processed using incorrect zero-copy and queuing assumptions.
WHY THIS VERDICT Attacks are confirmed. The vulnerability is 138 days old, so many systems are likely still unpatched. The severity score is critical (9.8).
WHY IT RANKS HERE Exploitation is confirmed by an authoritative source. 5 products are affected.
- HIGHEST CONFIRMED RUNG
- EXPLOITED
- CISA KEV
- LISTED
- EXPLOIT CODE
- PROOF OF CONCEPT CLAIMED
How far has it climbed?
01 TALK
▨ REPORTED, NOT CONFIRMEDNEWEST EVIDENCE · 1 SOURCECVE-2025-39964 discussed publicly (CIRCL sighting). CVE-2025-39682 discussed publicly (CIRCL sighting).
02 EXPOSED
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETWe have no source that counts exposed systems yet. Internet scan data needs a partnership we do not have. No evidence here does not mean nothing is exposed.
03 TRIED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESAttacks that worked are confirmed (step 4), so attempts count as confirmed too.
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability · SEP 17
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Race Condition Vulnerability · SEP 17
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Out-of-Bounds Write Vulnerability · SEP 17
- SRC: CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2026-53266 as actively exploited · JUN 25
04 EXPLOITED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESLinux Kernel contains an improper check for unusual or exceptional conditions vulnerability in the TLS receive path which allows a zero-length record retrieved from the rx_list to bypass the intended recvmsg() record-type handling, potentially causing subsequent TLS records to be processed using incorrect zero-copy and queuing assumptions. The impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version. Linux Kernel contains a race condition vulnerability which allows concurrent writes to the same AF_ALG socket causing data to be unpredictably interleaved and creating inconsistencies in the socket's internal state.
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability · SEP 17
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Race Condition Vulnerability · SEP 17
- SRC: CISA Known Exploited Vulnerabilities: Linux Kernel Out-of-Bounds Write Vulnerability · SEP 17
- SRC: CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2026-53266 as actively exploited · JUN 25
05 DAMAGE
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETBreach notices and filings rarely name the flaw that was used, so we cannot link them to this event yet. No evidence here does not mean no harm.
When each thing happened
- DISCLOSED
- EXPLOIT CODE PUBLICCLAIMED
- FIRST ATTACK REPORT
- CISA KEV LISTING
- US FEDERAL DEADLINE
THE FIX
CISA's instruction: apply the vendor's fix, or stop using the product if no fix exists. The deadline CISA set for US federal agencies, Sep 21, 2026, has passed. It is a US government deadline; use it as a guide.
Questions to ask this week
- Do we run Linux Kernel? If yes, is it patched or cut off from the internet?
- Who owns fixing it, and by what date?
- Have we checked for signs of attack since the first report, not just since the patch?
How it unfolded
- Attack activity. SEP 5, 2025CISA Vulnrichment marks CVE-2025-39682 as actively exploited
- Attack activity. OCT 13, 2025CISA Vulnrichment marks CVE-2025-39964 as actively exploited
- OCT 14, 20252 public GitHub repositories claim a proof of concept for CVE-2025-39682
- NOV 13, 20252 public GitHub repositories claim a proof of concept for CVE-2025-39964
- Attack activity. JUN 25, 2026CISA Vulnrichment marks CVE-2026-53266 as actively exploited
- Attack activity. SEP 17, 2026Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
- Attack activity. SEP 17, 2026Linux Kernel Race Condition Vulnerability
- Attack activity. SEP 17, 2026Linux Kernel Out-of-Bounds Write Vulnerability
- SEP 19, 20261 public GitHub repository claims a proof of concept for CVE-2026-53266
- NOV 10, 2026CVE-2025-39682 discussed publicly (CIRCL sighting) (2 reports)
- NOV 10, 2026CVE-2025-39964 discussed publicly (CIRCL sighting) (2 reports)
SOURCES
- [1] CIRCL Vulnerability-Lookup sightings: CVE-2025-39964 discussed publicly (CIRCL sighting), NOV 10
- [2] CIRCL Vulnerability-Lookup sightings: CVE-2025-39682 discussed publicly (CIRCL sighting), NOV 10
- [3] PoC-in-GitHub: 1 public GitHub repository claims a proof of concept for CVE-2026-53266, SEP 19
- [4] CISA Known Exploited Vulnerabilities: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability, SEP 17
- [5] CISA Known Exploited Vulnerabilities: Linux Kernel Race Condition Vulnerability, SEP 17
- [6] CISA Known Exploited Vulnerabilities: Linux Kernel Out-of-Bounds Write Vulnerability, SEP 17
- [7] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2026-53266 as actively exploited, JUN 25
- [8] PoC-in-GitHub: 2 public GitHub repositories claim a proof of concept for CVE-2025-39964, NOV 13
- [9] PoC-in-GitHub: 2 public GitHub repositories claim a proof of concept for CVE-2025-39682, OCT 14
- [10] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2025-39964 as actively exploited, OCT 13
- [11] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2025-39682 as actively exploited, SEP 5
- [12] CIRCL Vulnerability-Lookup sightings: 1 more reports