Answer in brief
CVE-2025-21655 records a Medium severity (CVSS 4.7) vulnerability in io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2025-21655 records a Medium severity (CVSS 4.7) vulnerability in io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 4.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=21a091b970cdbcf3e8ff829234b51be6f9192766 <6b63308c28987c6010b1180c72a6db4df6c68033 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <c9a40292a44e78f71258b8522655bffaf5753bdb | 6b63308c28987c6010b1180c72a6db4df6c68033, 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10, a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7, c9a40292a44e78f71258b8522655bffaf5753bdb |
| Linux/Linuxgeneric | 6.1 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
Published upstream
Jan 20, 2025
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.
Quoted source text, attributed separately from HOL analysis.
CVSS is 4.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=21a091b970cdbcf3e8ff829234b51be6f9192766 <6b63308c28987c6010b1180c72a6db4df6c68033 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7 || >=21a091b970cdbcf3e8ff829234b51be6f9192766 <c9a40292a44e78f71258b8522655bffaf5753bdb | 6b63308c28987c6010b1180c72a6db4df6c68033, 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10, a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7, c9a40292a44e78f71258b8522655bffaf5753bdb |
| Linux/Linuxgeneric | 6.1 | Not reported |
| Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
| Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric | >=V3.1.6 <* | * |
Published upstream
Jan 20, 2025
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Jul 14, 2026
In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.
Quoted source text, attributed separately from HOL analysis.